Brake device

A brake device comprising:

• a master cylinder;
• a braking mechanism configured to brake a wheel of a vehicle by a braking force;
• a hydraulic pressure circuit that couples the master cylinder to the braking mechanism;
• and
• a reservoir tank configured to store a hydraulic fluid of the master cylinder, wherein
• the master cylinder comprises:
• a housing having
• an interior space serving as a hydraulic pressure chamber, and
• a replenishing hole communicating with the reservoir tank;
• a piston configured to change a hydraulic pressure of the hydraulic fluid in the hydraulic pressure chamber by being moved with respect to the housing;
• and
• a seal member configured to seal a gap between the housing and the piston by being moved along with the piston,
• a first position, a second position, and a third position are positioned side by side in sequence as moving positions of the piston in a moving direction of the piston,
• the replenishing hole communicates with the hydraulic pressure chamber when the piston is at the first position,
• the seal member closes the replenishing hole when the piston is at the second position, and
• the hydraulic pressure of the hydraulic fluid in the hydraulic pressure chamber is made a negative pressure in a state in which the seal member closes the replenishing hole when the piston is at the third position.