A controller for a motorcycle brake system, the motorcycle brake system including: a brake operation section (11, 13) that is provided for a motorcycle; and a wheel braking mechanism (12, 14) that brakea a wheel (3, 4) of the motorcycle, the controller comprising: a brake operation execution section that initiates a braking force gentle increase operation in a state where the motorcycle makes a turn and input to the brake operation section (11, 13) is increased, the braking force gentle increase operation being executed to increase a braking force, which is generated by the wheel braking mechanism (12, 14), in a gentler positive gradient than the positive gradient in a case where the braking force on the wheel (3, 4), which is generated by the wheel braking mechanism (12, 14), depends only on the input to the brake operation section (11, 13); characterized in that the controller further comprises: a positive gradient setting section that sets the positive gradient in the braking force gentle increase operation, the brake operation execution section initiating the braking force gentle increase operation in the positive gradient, which is set by the positive gradient setting section when an initiation reference is satisfied, and a lean angle obtainment section that obtains a lean angle during turning of the motorcycle, wherein the positive gradient setting section sets the positive gradient that corresponds to the lean angle obtained by the lean angle obtainment section as the positive gradient in the braking force gentle increase operation. a brake operation section (11, 13) that is provided for a motorcycle; and a wheel braking mechanism (12, 14) that brakea a wheel (3, 4) of the motorcycle, the controller comprising: a brake operation execution section that initiates a braking force gentle increase operation in a state where the motorcycle makes a turn and input to the brake operation section (11, 13) is increased, the braking force gentle increase operation being executed to increase a braking force, which is generated by the wheel braking mechanism (12, 14), in a gentler positive gradient than the positive gradient in a case where the braking force on the wheel (3, 4), which is generated by the wheel braking mechanism (12, 14), depends only on the input to the brake operation section (11, 13); characterized in that the controller further comprises: a positive gradient setting section that sets the positive gradient in the braking force gentle increase operation, the brake operation execution section initiating the braking force gentle increase operation in the positive gradient, which is set by the positive gradient setting section when an initiation reference is satisfied, and a lean angle obtainment section that obtains a lean angle during turning of the motorcycle, wherein the positive gradient setting section sets the positive gradient that corresponds to the lean angle obtained by the lean angle obtainment section as the positive gradient in the braking force gentle increase operation. a positive gradient setting section that sets the positive gradient in the braking force gentle increase operation, the brake operation execution section initiating the braking force gentle increase operation in the positive gradient, which is set by the positive gradient setting section when an initiation reference is satisfied, and a lean angle obtainment section that obtains a lean angle during turning of the motorcycle, wherein the positive gradient setting section sets the positive gradient that corresponds to the lean angle obtained by the lean angle obtainment section as the positive gradient in the braking force gentle increase operation.