A brake control device is provided, which is capable of providing a precise diagnosis on a trouble on a hydraulic pressure valve etc., so as to provide an appropriate output hydraulic pressure corresponding to a stroke amount of a brake pedal. In this device, an electromagnetic valve is provided on a hydraulic pressure passage allowing an auxiliary hydraulic pressure chamber to communicate with an accumulator, and is controlled to open when such a trouble occurs that output hydraulic pressure from the hydraulic pressure valve becomes lower than a predetermined range; and an electromagnetic valve is also provided on a hydraulic pressure passage allowing the auxiliary hydraulic pressure chamber to communicate with a reservoir, and is controlled to open when such a trouble occurs that the output hydraulic pressure from the hydraulic pressure valve becomes insufficiently reduced.