To make a control body to be operated to actuate operation mechanisms unnoticeable from outside in a chair with the operation mechanisms such as a backrest rocking mechanism and a backrest height adjusting mechanism.

The control body to be operated with fingers by a user is disposed under an armrest 31, and a finger hook part 51 of the control body is movably supported in such a way as can approach to/separate from the upper surface of the armrest 31. A part of the lower side of the armrest 31 is notched to expose the finger hook part 51 to the outside while the control body is concealed from outside by a side wall 35 of the armrest 31. At the same time, the lower side of the armrest 31 and the lower side of the finger hook part 51 are structured to form the same continuous curved line or straight line as seen from a side when the control body is not operated.