PROBLEM TO BE SOLVED: To provide a chair achieving both of "allowing positional shifts between a hip part and a seating part, and between a waist part and a backrest part" and "changing a posture of a user", by one angle change operation of the chair in which the seating part having an elastic fabric stretched tightly thereon and the backrest part are integrally rotated about a rotation shaft arranged below a seating surface front part that projects upward, and achieving reduction in the number of components, and simplification.SOLUTION: A chair includes a seating part 11 on which a user S sits, and a backrest part 12 provided in the rear of the seating part 11. A seating surface 14 is formed by tightly stretching a seating elastic fabric D1 between left and right seating support frames 13 and 13, and a backrest surface 16 is formed by tightly stretching a back elastic fabric D2 between left and right back support frames 15 and 15. Further, a switching mechanism 19 is provided for changing an angle by integrally rotating the seating part 11 and the backrest part 12 about a rotation shaft 18 arranged below a seating surface front part 14a that projects upward.