PURPOSE: To measure a dynamic characteristic in an actual vehicle state by fitting a signal transmission means which transmits the signals from the strain gages to the outside measuring instrument to a drive-pinion shaft and calculating the dynamic characteristic of a clutch based on the signals from the strain gages.

CONSTITUTION: A boss part of a bearing retainer is cut and a slip ring 23 is fitted in this part in a body with the drive-pinion shaft 24. The brushes 28 of a bracket 27 are slid to the slip ring 23 but these brushes are connected with the slip ring 23 electrically and flocked vertically with respect to a brush arm 29 projected on the bracket 27. In this case, the three sets of strain gages 30 connected with the slip ring 23 electrically are stuck to the outside peripheral surface of the drive-pinion shaft 24 and the side end face of a retaining plate 32 at the equal intervals respectively. In this way, the dynamic characteristic of the clutch is measured in the actual vehicle state by securing the space to fit the strain gages and the signal transmission means.