To solve the problem that once a slip ring device has been assembled to an actual machine, a difference of contact potentials at a sliding part cannot be measured in an inner cylinder ring.

The slip ring device 1 includes: a plurality of stages of signal electrode rings 19; a plurality of brushes 23; a plurality of stages of power supply electrode rings 16 and 17; a cylindrical ring 26 for measurement provided below the power supply electrode rings 16 and 17; a first wiring material 28 drawn out upward through the inner side of the each power supply electrode ring 16 and 17; a second wiring material 31 which is short-circuited and folded back at the upper part, passes through the inner part of the each signal electrode ring 19, and is connected to one of the signal electrode rings 19 of a measuring target; and an auxiliary brush 33 which takes positions to be in contact with and separated to the ring 26 for measurement. The auxiliary brush 33 is brought into contact with the ring 26 for measurement and the signal electrode ring 19 of the measuring target energizes the sliding part between the outer peripheral surface of the rotating signal electrode ring 19 and the brush 23.