To surely prevent a table from being unexpectedly folded.

The table 50 is supported into a horizontal attitude flush with a top plate 14 by allowing a support member 70 to take an inclined support attitude of gradually ascending toward its tip and by applying an abutment part 71 positioned at the tip to a receiving part 65 on the back face. A stopper 75 which is positioned at a part toward a turning end of the back face of the table 50 and is provided with a locking part 76 for locking an abutment part 71 of the support member 70 in the support attitude, at an inward end and an operation part 77 at an outer end, respectively, is supported turnably around the shaft 82 of a hinge 80 between a locking position (a solid line) where the locking part 76 is locked to the abutment part 71 and a release position (a dotted line) where the locking part 76 releases the locking of the abutment part 71. The stopper 75 is constantly turnably energized to the locking position by the resilient force of a torsion coil spring 84. This constitution prevents a user from forgetting to lock the stopper 75 and surely prevents the table 50 from being unexpectedly folded.