PURPOSE: To make it possible to achieve measurement with simplcity and accuracy, by using a rim reference gage measuring member, which is able to be incorporated in a bearing, and a taper reference gage.

CONSTITUTION: A conical bearing, which is to be attached onto one end of an axis, is equipped with a rim reference gage 10 which was formed in a prescribed dimension instead of a rim of the bearing, and the small end side of the rim reference gage 10 is equipped with a measuring member 15 whose dimension in the axial direction toward the gage 10 is varied by the push-in force at the time when the bearing is pushed in. After these have been incorporated in the bearing device, the rim reference gage 10 and the measuring member 15 which is attached onto the gage are taken out from the bearing device and fit in a taper reference gage 30 which was formed in a prescribed dimension, and the axial gap of the conical bearing device is measured between the measuring member 15 and the taper reference gage 30.