PURPOSE: To effectively use the space inside a drum brake, to prevent foreign matters from being adhered to a sensor, and to facilitate the fitting work of the sensor.

CONSTITUTION: A sensor 25 to detect the rotation of a pulse rotor 22 rotatable between a pair of brake shoes 2, 3 is arranged between a back plate 10 to be mounted on a non-rotatable part of a vehicle and a web 3a to be formed in a brake shoe 3 which is movably arranged on the back plate 10. A through hole through which a shoe set pin 20 is passed is formed in the center part of the sensor 25, and upper and lower sides of the sensor 25 are flat and fixed by screws to the back plate 10. The body of the sensor 25 is not exposed outside, and foreign matters outside of the drum brake 1 are prevented from being adhered to the sensor 25. The sensor 25 is mounted on the drum brake 1 without interfering with the suspension.