There is provided a hydraulic fluid supply structure including: a discharge line fluidly connected to a discharge port of a hydraulic pump body and regulated to have a first pressure value; an external hydraulic fluid extraction line for supplying the hydraulic fluid to an actuator for raising and lowering a working machine, the external hydraulic fluid extraction line being fluidly connected to the discharge line through a resistance valve; a PTO hydraulic fluid line for supplying the hydraulic fluid to a hydraulic operating type clutch mechanism for engaging or disengaging power transmission to the working machine, the PTO hydraulic line being fluidly connected to the discharge line through a throttle valve and regulated to have a second pressure value lower than the first pressure value; and a PTO switching valve interposed in the PTO hydraulic fluid line so as to turn ON/OFF the supply of the hydraulic fluid to the hydraulic clutch mechanism. The PTO switching valve is configured to block a primary side line, out of the PTO hydraulic line, positioned on the upstream side from the PTO switching valve, when the supply of hydraulic fluid to the hydraulic clutch mechanism is turned OFF.