To smoothly elevate and lower a seat and to maintain a height without changing it once it is set regardless of a load on the seat.

This seat mechanism is provided with a vertically movable seat 7.1 and an extendible/contractible lift column 1 for supporting the seat 7.1 and the column 1 is composed of interacting members 1.1, 1.2, 1.3 and 1.4 provided with two terminating end members and at least one center member between them. At least the center member and a first terminating end member are provided with male screws, at least the center member and a second outer side member are provided with female screws and a driving device 3 connected to one terminating end member capable of rotating the members in both directions around a long axis is installed.