To use a connecting shaft also as a guiding member for a snap bar by forming the connecting shaft with the link of a door body for attaching the snap bar to be hollow and housing the snap bar in this hollow part to be freely moved up and down.

A snap bar 15 is housed so as to be freely moved up and down in the hollow part of a hollow vertical shaft 4 in a vertical frame 2a and protruded from a through-hole provided in a pulling-out preventing washer 13 provided fixed in the lower end part of the hollow vertical shaft 4. By moving a knob 16 up and down, locking and unlocking are operated from the outside of the vertical frame 2a. A female screw is formed to penetrate the snap bar 15 and, by twist-screwing in the knob 16 to a limit, the snap bar 15 is fixed in an optional position. In an expansion door 1, since the snap bar 15 is housed in the hollow part of the hollow vertical shaft 15 for connecting a linking member 3 with a door body 2, it is not necessary to attach the guiding member of the snap bar 15 to the door body 2 and thus the weight of a gate door is reduced and appearance designing is improved.