A brake system includes a master cylinder which generates brake fluid pressure by a braking operation of a driver, an electric motor driven slave cylinder that generates brake fluid pressure according to an electrical signal based on the braking operation of the driver, a vehicle wheel cylinder for braking a wheel by the brake fluid pressure generated in the master cylinder or the slave cylinder, a brake light that informs a following vehicle of the operation of the wheel cylinder, and a first sensor and a second sensor that detect stroke positions of the brake pedal. During normal operation of the brake system the brake fluid pressure generated in the slave cylinder is transferred to the wheel cylinder. During abnormal operation of the brake system, the brake fluid pressure generated in the master cylinder is transferred to the wheel cylinder. Further, the first sensor activates the brake light when the slave cylinder operates normally, and the second sensor activates the brake light when the slave cylinder does not operate normally.