Is working memory equivalent to fluid intelligence? Some report indicates that working memory capacity is equal to the g factor, so I'm wondering what is actual point of view on this among psychologists.

Colom, R., Abad, F. J., Rebollo, I., &amp; Shih, P. C. (2005). Memory span and general intelligence: A latent variable approach. Intelligence, 33, 623–642.
I would not go as far as saying that working memory (WM) is equal to g factor (gf). WM only accounts for 38% of variation in gf performance whether is no time pressure, this is not insignificant but it important to consider that holding information is important for any gf task. It has perviously been considered that the complexity of information required in different gf tasks would depend on WM capacity. For those that do not know: working memory (WM) is basically the capacity of information an individual can temporally hold at any one time. Anyhow the notion that complexity takes up more working memory and therefore is predictive of gf performance, in other words holding information in WM is thought to help us analyse and break it down to solve problems such as posed in gf tasks. This notion is does not appear to be supported, with research finding that the correlation between gf and WM being relatively consistent across task complexities. 

So what is the function of this relationship? A 2011 fMRI study by Burgess et al strongly suggests that the relationship between WM and gf is to do with interference control, in their words..."Our findings suggest that the relationship between WM span and gF can be linked, at least in part, to a common dependence on mechanisms of interference control that reflect activation in a core set of brain regions centered on the lateral PFC and parietal cortex...these regions [are] fairly specific and selective in their predictive utility for explaining common variance in gF and WM span...We theorize that the exact brain regions and processes related to gF and WM span will likely depend upon the nature of processing required during the task, and the temporal dynamics of those task demands." Simply, the primary function of the relationship WM capacity and gf appears to be to focus on task. Interestingly from the area of hedonics we know that WM is predictive of how likely an individual is to respond their environment and motivational prompts such as food or alcohol. These motivational cues can be considered interference from long term goals such as avoiding eating or maintaining sobriety.