A disc brake has a brake caliper which straddled a brake disc and is mounted on a stationary brake carrier so as to be axially movable in relation to the brake disc. Brake pads which are placed in the brake caliper can be pressed against the brake disc by a brake application mechanism during a braking operation. In order to be axially movable, the brake caliper is mounted on at least one guide bar that is connected to the brake carrier. A device is provided for optically detecting wear of a brake disc and/or a brake pad. In order for wear to be detectable, a comparative element which runs parallel to the guide bar, extends away from brake disc, and includes at least one step, is mounted on the brake carrier.