A PTO control system for allowing selection between an independent PTO mode and an interlock PTO mode, comprising a mode-switch command input device 11 for giving an instruction on selection between the independent PTO mode and the interlock PTO mode, a PTO setting device 12 having an engaging position for producing an engaging command and a disengaging position for producing a disengaging command of the PTO clutch, and a PTO control unit for controlling a PTO clutch in response to a pedal operational position of a brake pedal, a mode selected by the mode-switch command input device, and a position selected by the PTO setting device. PTO mode switch implementation processing is suspended when the PTO transmission system is in a power transmittable state, while the PTO mode switch implementation processing is permitted when the PTO transmission system is in the power non-transmittable state.