A top surface of a transmitter on a torque wrench is opposed to a position camera, and bolt holes to fix the transmitter to a wrench main body open on the top surface. The bolt holes are formed to four places so as to define a rectangle and extend in a thickness direction of the transmitter. The marker is attached to the top surface of a head of one of the bolts, which extends through a through bolt hole. When the transmitter is fixed to the main body using a bolt, the depth of a large diameter portion of the through bolt hole is larger than the total thickness of the bolt head portion and the marker. Therefore, the marker is disposed lower than an aperture surface of the bolt hole and the possibility of the marker being damaged during work is reduced.