A method for detecting fluid leakage from a pressure-decrease valve in a hydraulic brake system having an ABS device (18) including: a shutoff valve (140) for shutting off supply of a working fluid from a fluid-pressure supply source to a brake device (12) provided for a wheel; the pressure-decrease valve (142) for discharging the working fluid from the brake device; a reservoir (146) for storing the working fluid discharged from the pressure-decrease valve; and a return pump (154) for returning the working fluid stored in the reservoir to a portion between the shutoff valve and the fluid-pressure supply source, the method including the steps of: activating the return pump in a state in which the hydraulic brake system is not in ABS operation, and detecting the fluid leakage from the pressure-decrease valve based on a variation in a pressure of the working fluid in the fluid-pressure supply source caused when the return pump is activated.