PURPOSE: To improve reliability by using a prevention sensor for preventing the damage of a seat moving along a stool seat frame.

CONSTITUTION: A stool seat device 1 is provided a stool seat frame 5, a taking out port for drawing a seat 6 and a seat feeding means 9 on a base body 3 attached to a stool 2 and a control means 11 with a prevention sensor preventing the damage of the seat 6 is attached thereto. The control means 11 is constituted of a mark sensor 90 for detecting a fixed dimension mark 28 provided on the seat 6 and a prevention sensor 91 consisting of a sitting sensor 91A for detecting the sitting of a user to the stool seat frame 5 and a stool seat frame sensor 91B for detecting the jumping of the stool seat frame 5 and they respectively operate or stop motors M, m through a control circuit 92. The mark sensor 90 detects the change of the amount of received light caused by the passing of the fixed dimension mark 28. The sitting sensor 91A detects the decrease in the amount of received a light caused by the closing of a through hole 95A due to the sitting of the user and the stool seat frame sensor 91B detects the decrease in the amount of received light generated from the overlap of a through hole 95B and a case cover 31 due to the jumping of the stool seat frame 5, respectively. Thereby, troubles such as the break, the extension of the seat 6, the winding thereof the seat feeding means 9 can be prevented.