In case the seat portion of the inclining chair is inclined periodically, if a supporting shaft to incline the seat portion is arranged away from a position supporting an ischial tuberosity portion of a seated person in an ordinary posture of sitting, an upper body of the seated person makes an up and down movement widely in compliance with a periodical inclining movement of the seat portion, which might cause dizziness due to a vertical shock to the upper body of the seated person. The supporting shaft 61d to incline the seat portion 3 periodically is arranged near an ischial tuberosity portion HB of a seated person in an ordinary sitting posture, namely, at the rear of a center CL1 along a back and forth direction of the seat portion 3. More specifically, the supporting shaft 61d is arranged within a range of 50 mm to 180 mm in front of a front face of a backrest so that fatigue of a hip, a femur, a lumber and a back and tumefaction of a lower limb of a seated person are mitigated and occurrence of dizziness is reduced as well.