PURPOSE: To provide a working oil tank installation structure of an industrial vehicle with which the cooling effect for the working oil can be improved and the arrangement work for the hydraulic piping related to the working oil tank can be made simple.

CONSTITUTION: A working oil tank 1 is formed on a separated body which is independent from the side plate 2 of a machine base frame. The working oil tank 1 is fixed, keeping a certain interval, through a tank bracket 3 for the outside surface of the side plate 2. Accordingly, an air flow space 4 is formed between the side plate 2 and the working oil tank 1, and the contact area of the working oil tank for the outside air is increased, and the cooling action for the tank is positively carried out by the air passing through the flow space. Further, a hydraulic piping 7 is arranged in the flow space on the outside of the side plate, and the arrangement work, etc., can be carried out from outside the side frame, and the piping is protected by the tank bracket.