The present invention relates to a trunk support cushion disposed on a seat of a wheelchair or a chair, comprising: a first cushion portion positioned on a front surface of a backrest； and a second and third cushion portions connected to left and right respective side portions of the first cushion portion and positioned on inner side surfaces in the vicinity of elbow rests, the cushion being formed such that the first cushion portion is fixed to the backrest side by causing a first attachment member such as a belt to apply a tension force bringing the first cushion into contact with the backrest and that the second and third cushion portions are fixed to frames or support posts provided with the elbow rests by causing second and third attachment members forming a belt shape extending forward from front end portions thereof to apply a forward tension force to the second and third cushion portions while appyling a forward tension force via the second and third cushion portions to the first cushion portion.
