The management gender pay gap stands at an average of £3,188 - or 13%.
Although this is less than the UK average of 22%, the Chartered Management Institute (CMI) said it was still "unacceptable".
The findings are in its annual salary survey of more than 72,000 professionals across the UK.
How big is the gap?
The findings are reflected in the most recent Office for National Statistics (ONS) figures. These show women in professional occupations in Wales received an average of £678 gross pay a week in 2014  - compared to men on £794 a week.
That 15% gap also exists between women and men's pay across all sectors in Wales - and has remained largely unchanged for a decade.
It is slightly better than the UK average - 20% and 19% if you exclude London and the south east.
The ONS said it was a complex issue and prefers we look at median hourly earnings for those in full-time work, which suggests the pay gap is now the lowest on record.
It is now 9.4% between all working men and women - around £100 a week - compared to 17.4% in 1997.
Why does the pay gap exist?
Cardiff University researchers last year found the working patterns of men and women are very different.
"Feminised" jobs attract lower hourly pay rates and have high concentrations of part-time hours, it suggested.
In summary:
The university research team claimed, with little training or career progression opportunities, women can get "stuck" in these working patterns for life.
ANALYSIS by Sarah Dickins, BBC Wales economics correspondent
Forty five years after the UK Government passed the Equal Pay Act, working women in Wales are still earning on average more than £3,000 less than men.  In effect they are working for 34 days each year for free.
In Wales the gap between what men and women earn is less - at 13% - than for the UK as a whole, which is 22%. On the face of it, that may seem to be good news and could be used to suggest that Wales is a more equal society. But it could also be seen as a reflection of the fact that the Welsh economy has relatively fewer high paid jobs across many aspects of the private sector.
Today's report highlights the fact that the gap between what men and women are paid is greatest at the senior or director level and greater as women grow older.
Q&A: How can we bridge the gender pay gap?
Prime Minister David Cameron has pledged to eliminate the gender pay gap "within a generation".
New legislation coming into force in 2016 will require organisations with 250 or more staff to report publicly what they pay male and female staff.
On Monday, accountancy firm Deloitte revealed it paid women on average 17.8% less than its male workers,  but said there was an "ever increasing understanding" of the issues.
The CMI wants more companies to publish gender pay details before they have to next year, as well as reviewing starting salaries to ensure problems do not start at the recruitment stage.
But attempts at increasing the number of women executives in UK boardrooms appear to be working.
The latest progress report by Welsh banker Lord Mervyn Davies  showed the number of women holding board-level positions in FTSE 100 companies reached 23.5% - just short of a 25% target.
His report highlighted two Welsh companies doing better for the representation of top-level women.
Cardiff-based Admiral has five women executives on its 12-strong board and is ranked third in the top 100. From the top 250 companies, Flintshire-based Redrow has three women out of seven board members.
Paul Thomas of CMI's Wales board said: "While some progress is being made, it's clear from our research that Lord Davies is right to target the executive pipeline.
"Having more women in senior executive roles will pave the way for others and ensure they're paid the same as their male colleagues at every stage of their careers."
Women managers in Wales are effectively working for free for nearly an hour every day, a professional body claims.