A brake system including a slave cylinder for generating a fluid pressure by an electric actuator which is driven based on a traveling amount of a brake operator, comprising: a fluid line (2a, 2b, 4, 5a, 5b) which establishes a communication from the slave cylinder to wheel brakes (FL, RR, RL, FR); a cutoff valve (61, 62) which is provided on the fluid line (2a, 2b, 4, 5a, 5b) and which can cut off the fluid line (2a, 2b, 4, 5a, 5b); a reservoir tank for reserving brake fluid; a supply line for supplying the brake fluid from the reservoir tank to the slave cylinder; and a control unit which executes a fluid suction control to suck in the brake fluid from the supply line, wherein the control unit determines whether or not the fluid suction control needs to be executed, and in the event that the control unit determines that the fluid suction control needs to be executed, the control unit executes a control in which the cutoff valve (61, 62) is closed and the slave cylinder is driven in a depressurizing direction by the electric actuator, and wherein the supply line is connected to the fluid line (2a, 2b, 4, 5a, 5b) by way of a branch supply line and a check valve is provided on the branch supply line, the check valve being configured to permit only a flow of the brake fluid from the reservoir tank to the slave cylinder, wherein in the event that the amount of the brake fluid in the slave cylinder is reduced as a result of depressurizing the wheel brakes (FL, RR, RL, FR), the control unit executes a control as the fluid suction control in which the cutoff valve (61, 62) is closed and the slave cylinder is driven in a depressurizing direction by the electric actuator, characterized in that: the brake system further comprising a road surface friction coefficient estimation module for estimating a road surface friction coefficient during an anti-lock braking control, wherein the control unit changes a timing at which the fluid suction control is executed based on a road surface friction coefficient which is estimated by the road surface friction coefficient estimation module. a fluid line (2a, 2b, 4, 5a, 5b) which establishes a communication from the slave cylinder to wheel brakes (FL, RR, RL, FR); a cutoff valve (61, 62) which is provided on the fluid line (2a, 2b, 4, 5a, 5b) and which can cut off the fluid line (2a, 2b, 4, 5a, 5b); a reservoir tank for reserving brake fluid; a supply line for supplying the brake fluid from the reservoir tank to the slave cylinder; and a control unit which executes a fluid suction control to suck in the brake fluid from the supply line, wherein the control unit determines whether or not the fluid suction control needs to be executed, and in the event that the control unit determines that the fluid suction control needs to be executed, the control unit executes a control in which the cutoff valve (61, 62) is closed and the slave cylinder is driven in a depressurizing direction by the electric actuator, and wherein the supply line is connected to the fluid line (2a, 2b, 4, 5a, 5b) by way of a branch supply line and a check valve is provided on the branch supply line, the check valve being configured to permit only a flow of the brake fluid from the reservoir tank to the slave cylinder, wherein in the event that the amount of the brake fluid in the slave cylinder is reduced as a result of depressurizing the wheel brakes (FL, RR, RL, FR), the control unit executes a control as the fluid suction control in which the cutoff valve (61, 62) is closed and the slave cylinder is driven in a depressurizing direction by the electric actuator, characterized in that: the brake system further comprising a road surface friction coefficient estimation module for estimating a road surface friction coefficient during an anti-lock braking control, wherein the control unit changes a timing at which the fluid suction control is executed based on a road surface friction coefficient which is estimated by the road surface friction coefficient estimation module. the brake system further comprising a road surface friction coefficient estimation module for estimating a road surface friction coefficient during an anti-lock braking control, wherein the control unit changes a timing at which the fluid suction control is executed based on a road surface friction coefficient which is estimated by the road surface friction coefficient estimation module.