PURPOSE: To easily and surely adjust a breadthwise space between armrests in a good balance while the user is seated with his/her elbows on the armrests.

CONSTITUTION: When a motor is rotated via a switch, the rotation thereof causes the interlocked right and left symmetrical motion of respective armrests 4 fastened to the ends of a support member 6 through an interlock means. Also, the reverse motion of both armrests 4, if desired, can be realized by reversing the motor via the switch. Consequently, a user can symmetrically move the right and left armrests 4 at equal intervals simply via the one-hand operation of the switch, with his/her arm placed on one or both of right and left armrest 4. Thus, the breadthwise space between both armrests 4 can be easily and property adjusted in a good balance.