PURPOSE: To suppress forced displacement fluctuation which occurs in a chain on the occasion of transition between linear track and curved track so that vibration application force is not input in a chain guide.

CONSTITUTION: A contact face 10A of a chain guide in contact with a chain is constituted by a curved track forming section 10a and linear track forming sections 10b, 10c adjacent to its start point S and end point E. The linear track forming sections 10b, 10c are offset in parallel by a distance represented by an equation, =(R+d/2)-{(R+d/2)2-(L/2)2}1/2, in the direction in which they are apart from a center of curvature 0 of the curved track forming section 10a from a tangent line 20 at the start point S or a tangent line at the end point E.