PURPOSE: To make visual recognition of the travel process of a reciprocating cylinder within a single and the same display range possible by continuously transmitting the torque of a rotary body of the driving side to the rotary body of the driven side while making the rotary body of the driven side to intermittently rotate at the time of reverse rotation.

CONSTITUTION: When a rotary body 22 of the driving side rotates in a linked motion with a drive shaft of a hydraulic pump or the like, a timing lever 31 is not obstructed by a guide body 34 and maintains the condition of contact with engagement pins 30a, 30c. As a result, the torque of the rotary body 22 of the driving side is continuously transmitted to a rotary body 25 of the driven side. When the rotation is reversed, a guide body 34 comes in contact with the tip of a timing lever 31 so that it is guided to separate from engagement pins 30a-30c along the guide body 34. As a result, the continuous rotation of the driving side rotary body 22 is intermittently transmitted to the driven side rotary body. As a result, the amount of the advance of a display hand 23 changes depending on the directions of the rotation.