PURPOSE: To guide a cam follower through an intersection of a cam track by radially reciprocating a pair of crossover cams, and making them enter and leave the intersection of the cam track in an insert form in synchronism with the passage of the cam follower to the intersection.

CONSTITUTION: When a segment 66 of an outer crossover cam member 44 is radially inserted into an intersection by the action of lobes 54, 58 to be displaced in relation to the diametral direction, the lobe 54 is engaged with the upper part 56a of an opening part 56 to radially retract a segment 62 of an inner crossover cam member 48 from the intersection to a lower stationary position. While, when the segment 62 is radially inserted into the intersection, the lobe 58 is engaged with the lower side part 60b of an opening part 60 to retract the segment 66 to a lower stationary part, and therefore, the cam follower to be moved in a cam track part 28 can pass through the intersection.