A trunk width measuring unit including a first contact portion attached movably in the vertical direction relative to a unit main body, the first contact portion to be brought into contact with an upper surface of a trunk of a subject, second and third contact portions attached movably in the horizontal direction relative to the unit main body, a vertical width detection encoder for detecting a lowering distance of the first contact portion from an original position on the upper side of the trunk of the user to a contact point with the upper surface of the trunk, and a horizontal width detection encoder attached movably in the horizontal direction relative to the unit main body by the same distance as a moving distance of the second contact portion, the horizontal width detection encoder detecting a moving distance of the third contact portion relative to the second contact portion.
