To allow a seat turning mechanism to keep a rotation regulation effect without receiving a significant effect on use and collapse of a resin though it has a simple structure.

The seat turning mechanism has a seat frame 1 to which a seat 23 is attached and a seat turn supporting rod 6 turnably supporting the seat frame 1. A first receiving member 7 and a rotation stopping portion 8 provided in the seat turn supporting rod 6 with a space interposed therebetween, a second receiving member 2 provided in the seat frame 1 and arranged between the first receiving member 7 and the rotation stopping portion 8, a turning shaft 3 penetrating the first receiving member 7 and the second receiving member 2 and tightening the first receiving member 7 and the second receiving member 2 as if to pinch them and having a head 3a at one end and a turning shaft stopper 5 fitted into the opposite side of the head 3a of the turning shaft 3, an abutting face 11 prepared in the rotation stopping portion 8 abutting against the side of the head 3a of the turning shaft 3 and inhibiting the relative rotation of the turning shaft 3 with respect to the seat turn supporting rod 6. The rotation stopping portion 8 allows the head 3a of the turning shaft 3 to axially pass therethrough.