Abstract: A shift guide structure of a transmission includes a guide pin located on one of a shift-and-select shaft and a case, the shift-and-select shaft being supported by the case and axially and circumferentially movable; and a guide plate located on the other of the shift-and-select shaft and the case, the guide plate being provided with a path for guiding the guide pin between positions corresponding to gears. The guide pin includes a cylindrical part. The guide pin includes an insertion to be inserted into the path. A cross section of the insertion includes an outer circumferential edge that includes two mutually parallel linear parts with spacing smaller than an outer diameter of the cylindrical part, and two projections that connect ends of the two linear parts. The projections each include a curved part having a radius of curvature smaller than a radius of the cylindrical part.