To prevent a finger or the like from being caught between a recess in the lower surface of the armrest of a chair and an armrest support member even when the armrest is moved to a longitudinal limit position.

A longitudinally facing recess 3b is formed in the lower surface of an armrest 3 and guide grooves in guide members 24 provided on both right and left sides of the recess 3b are slidably fitted over both right and left sides of an armrest support member 21. Stoppers 24b, 21c for regulating the range of longitudinal relative movement between the armrest 3 and the armrest support member 21 are provided between the guide members 24 and the armrest support member 21. When the armrest 3 is moved to a longitudinal limit position, a gap of the required size is formed between a longitudinal end of the recess 3a and a longitudinal end face of the armrest support member 21.