the mouse has a housing (12) with at least one operating button (18) and contg. a ball (26) whose movement can be detected by a detector (38) in the housing. Each detector has a light source (34) and associated light sensor (36). The light sensors are protected against the incidence of stray light by a screening cover (22) in the form of a cap mounted within the housing. The housing and operating button are also screened by a cover.
