To provide a brake system, which can realize both a low cost structure and high regeneration efficiency and realize brake characteristics corresponding to the stroke of a brake pedal and free of sense of incongruity.

A brake system employs a low cost structure, wherein a negative pressure actuator 40 which relieves the stepping displacement of a brake pedal 1 via a balance mechanism 34 is provided in parallel with a master cylinder 10 having a negative pressure booster 10a, which generates a braking force by the stepping displacement of the brake pedal, and further, a solenoid valve 60 is provided in an atmosphere outlet 33 of the negative pressure booster 10a and the stepping displacement of the brake pedal 1 is shared between the master cylinder 10 and the negative pressure actuator 40 according to the operation ratio of a mechanical brake. With this constitution, high regeneration efficiency can be obtained at regenerative braking, and when mechanical braking becomes necessary, braking force generated by the mechanical brake is made to be applied regardless of the stop on displacement of the brake pedal 1.