Disk brake

The present disclosure provides a disk brake capable of making it easier for the piston to return than conventional ones when the brake is released from a state where the brake is applied. In the disk brake, the seal groove 5 includes a front wall 51, a rear wall 52 farther from the brake rotor than the front wall 51 in the axial direction Dl, and a bottom wall 53 extending along the axial direction Dl between the rear wall 52 and the front wall 51. The bottom wall 53 includes a front bottom wall 53a adjacent to the front wall 51 and a rear bottom wall 53b adjacent to the rear wall 52. The rear bottom wall 53b has a depth d2 from the inner circumferential surface 42a of the cylinder 42, the depth d2 being larger than a dimension d3 of the uncompressed piston seal 6 in the direction of the depth d2 and being larger than a depth d1 from the inner circumferential surface 42a of the cylinder 42 of the front bottom wall 53a.