PURPOSE: To increase or decrease the number of seats easily by mounting the detachable seats.

CONSTITUTION: A horizontal hole 9 is formed in a seat frame 2 in a fixed seat pad 1, and a leg hole 19 is made up to a lower section of a leg 3. A horizontal bar 11 is mounted to a detachable seat pad 6, a horizontal bar 11 is inserted into the horizontal hole 9 while supporting arms 8 are installed by means of bolts 21, 22, and seat frames are mutually fixed by means of a bolt 15 and a nut 17, thus mounting the detachable seat pad 6 to the fixed seat pad 1. The length of the supporting arms 8 can be adjusted by means of a turnbuckle 7. The number of seats can simply be increased or decreased because the seat pads can be detached by simple operation.