To provide a fluid pressure brake device capable of always displaying sufficient vehicle braking force.

An ECU detects energization limit pressure PLIM of master cylinder pressure PM/C by a brake booster 12. This energization limit pressure PLIM is determined according to the size of booster negative pressure acting on the brake booster 12 from an intake manifold 20 of an internal combustion engine 18 via a negative pressure conduit 22. The ECU makes a solenoid valve 34 and pressure reducing solenoids 52, 54 closing valve states, makes a solenoid valve 36 and holding solenoids 40, 42 opening valve states, performs a braking auxiliary control making a pump 62 into an operating state and boosts wheel cylinder pressure PW/C to a value higher than master cylinder pressure PM/C, when master cylinder pressure PM/C exceeds limit pressure PLIM. The ECU switches the internal combustion engine 18 from stratified charge combustion to homogeneous combustion when the braking auxiliary control can not be performed.