PURPOSE: To reduce arm weight acting on the shoulders as well as a burden on the waist for supporting the upper body by forming an armrest out of an arm placement board having a shape and a size suitable for supporting an elbow, and a mounting fixture.

CONSTITUTION: An arm placement board 2 having a shape and a size suitable for-supporting the section of an arm forward of an elbow is mounted on a desk top plate 1 via a mounting fixture 3. For the operation of a computer keyboard, the vicinity of the elbow is placed on the front section of the body of the board 2 and then the keyboard is operated. According to this construction, the keyboard can be quickly operated without reducing a work speed, and the fatigue of the shoulders and waist due to a long-time operation can be lessened.