Support the seater to ensure that the posture is appropriate.Solution: a first support portion (23) of a concave spherical curved surface shape capable of supporting a buttocbed portion (42) of a sitting state, a front protruding portion (24) projecting forward from the lower end of the first support part (23) and supporting the lower side of the thigh (43), and the upper side of the first support part (23), and the waist (44) An upper protrusion (25) is provided with a lumbar support portion (28) having a convex curved shape capable of supporting an ilium (151) portion of the ilium.A first arcuate portion (30) is formed on both sides of the root portion of the upper projecting portion (25).Diagram【課題】着座者をその姿勢が適正になるようにサポートする。【解決手段】着座状態の臀部（４２）を支持可能な凹状の球状曲面形状の第１支持部（２３）と、その第１支持部（２３）の下端から前方に突出し、太腿（４３）の下側を支持可能な前部突出部（２４）と、第１支持部（２３）の上側に位置し、腰部（４４）の腸骨（１５１）部分を支持可能な凸状湾曲形状の腰部支持部（２８）を備えた上部突出部（２５）とを備える。上部突出部（２５）の付け根部の両側には、第１抉り部（３０）を形成する。【選択図】図４
