Matthew Gordon said he never "cut corners" when it came to maintenance and spent more than Â£6,000 in a year on repairs to the truck.
He told Bristol Crown Court if the lorry had been unsafe he "would have done something about it".
Mr Gordon, 30, of Dauntsey, Wiltshire, denies 14 charges against him.
Mr Gordon, the owner of Grittenham Haulage, is defending himself following the crash on Lansdown Lane on 9 February last year.
Mitzi Steady, four, Robert Parker, 59, Philip Allen, 52, and Stephen Vaughan, 34, died in the crash in 2015.
The lorry hit several pedestrians, including Mitzi, from Bath, and a car containing Mr Allen and Mr Vaughan, both from Swansea, and Mr Parker, from Cwmbran, south Wales.
Driver Phillip Potter, 20, also of Dauntsey, denies causing the deaths by dangerous and careless driving. He is also charged with causing serious injuries to Karla Brennan and Margaret Rogers - Mitzi's grandmother - by dangerous driving.
He denies a total of 10 charges against him.
Peter Wood, 55, from Brinkworth, Wiltshire, a mechanic who carried out safety checks on the truck, denies four charges against him.
The trial continues.
The owner of a lorry that crashed on a steep hill in Bath killing four people has told a jury he did not think the vehicle was unsafe that day.