A chair with freely attachable and removable armrests comprises a basic chair unit wherein a leg and a back rest portion attached to a frame on a lower surface of a seat portion, the two ends of the lower surface in the lateral direction of the seat portion being provided with armrest attachment portions. An attachment end portion provided at the lower end of each armrest comprises a positioning protrusion portion that can be inserted into a positioning hole provided in an internal portion of one of the armrest attachment portions. An attachment base portion (spacer) is positioned and held in close contact with guide surfaces along a guide portion of the armrest attachment portion, and a removal-prevention element in the armrest attachment portion is provided for preventing the removal of the attachment end portion. Thus, armrests can be removed from the basic chair unit by a simple operation.