In the conventional connection and fixture part between a working vehicle and an excavator, a connection pin is made to contact a guide plate to be fixed in position, thereby requiring a high rigidity of the guide plate, accuracy of recreation of positioning of the connection pin, and high cost for manufacturing the guide plate. Thus, a guide plate of a connection portion has a chevron-shaped introduction part including two sector curves. A U-shaped bent member serving as a knob is provided on a rear side surface of a connection pin in the axial direction of the connection pin, so that the proper position of the inserted connection pin is defined as the position thereof when tips of the knob come into contact with the insertion-target member.