To provide a chair having the primary function of a chair with a backrest for holding the back of a seated person, allowing the seated person to sit down from any direction and completely accommodated under a desk, or the like.

This chair is provided with a backrest part 21 rotatable in relation to a seat part 11 around a fulcrum S within a designated angle range, and a backrest locking means 41 capable of locking the backrest part 21 on either an erect position P1 for holding the back of a seated person or an accommodating position P2 in front of the erect position P1 and lower than the seat part 11.