To improve the sliding characteristic and reliability while eliminating the powdery material of a slide-contact surface during the operation of a gear by providing a recessed part capable of housing the powdery material at a position crossing the moving locus of the powdery material in at least one of a main surface of the gear and a slide-contact member having a surface sliding with the main surface.

This gear mechanism has two spur gears 1a, 1b, and grooves 2a-2c are provided on slide-contact surfaces thereof, and these grooves are formed into an annular shape concentrically with a rotary shaft of the spur gear 1a, and the groove 2c is formed into an annular shape concentrically with a rotary shaft of the spur gear 1b. Grooves 3a-3c are provided on a housing 4 for sliding-contact with the spur gears 1a, 1b. These grooves are formed into an annular shape concentrically with the rotary shaft of the spur gear 1a. Since the powdery material to be moved with the rotation of the gear can be securely caught for elimination in a moving process thereof, sliding characteristic of the gear mechanism can be securely improved.