PURPOSE: To provide a size measuring device capable of accurately measuring the thickness and height of circular projections and recesses existing on part of a measured object on the whole periphery, not partially, and capable of fully satisfying operability and economical efficiency.

CONSTITUTION: A measured object 3 is held on a turntable 4 by a holding means 14. A sliding base 16 is advanced toward the turntable 4 by a sliding base driving means, then a probe 29 is rotated by a probe driving means 30, the tip of the probe 29 is brought into contact with the upper face or the lower face of a projection 5 or a recess 5a, and the displacement of the probe 29 by rotation is detected by a displacement sensor 31. The measured object 3 is rotated by the turntable 4, and measurement can be made on the whole periphery while the measurement station is changed.