PURPOSE: To improve the surface accuracy in finishing of gear by machining a gear material in the direction of tooth trace performing minute reciprocating slide in addition to the machine in the direction of the tooth profile.

CONSTITUTION: The machining of a gear material in the direction of tooth trace is performed by a tool T with the tool carrier 1 holding the tool T minutely performing reciprocating slide by means of a slide drive device 3. The device 3 is provided with drive shafts 30 and 31 having eccentric shafts 30a and 31a respectively. The synchronized rotation of the shafts 30 and 31 makes the tool carrier 1, that is, the tool T perform reciprocating slide minutely with twice stroke as much amount as eccentricity of eccentric shafts 30a and 31a. Since the tool T is reciprocated being rotated to machine a tooth face in both the length and width directions, a high accurate machined surface can be obtained.