A brake actuator comprising a sleeve (1), a piston (3) sealingly slidably mounted in the sleeve to apply a braking force, the piston being provided with an internal cage (21), and a wear compensating device (10) which defines a retracted position of the piston in the sleeve by means of an axially mobile stop which is able to be moved forward by the piston during the application of a braking force and/in frictional relationship with a fixed part (12) of the wear compensating device attached to the sleeve. The mobile stop comprises a radially deformable bushing (16) which cooperates with an olive (15) which is attached to a distal end of the fixed part of the wear compensating device. The bushing comprises means for guiding its proximal end (17) against an internal face of the internal cage (21).