To surely absorb vibration of low frequencies and efficiently prevent vibration.

A step part and a seat are integrally supported with a supporting body which utilizes a pantograph mechanism for preventing vibration and supporting. The pantograph mechanism is equipped with a pair of links whose middle parts are pivoted by an axle and a spring arranged between the both links to extend and contract in an approximately horizontal direction. Also, the spring is provided so that the horizontal width becomes narrower as compared with a vertical size before an operator sits on a seat, and the horizontal width becomes wider compared with the vertical size after the operator sits on the seat.