PURPOSE: To generate irregular delay time to the measurement of the machined diameter of a measured part in the depth direction of a bore and also to the measurement of the depth position of the measured part.

CONSTITUTION: A honing head 11 is provided with a first air nozzle 55 for jetting air to the bore inner surface Ha. A first converter 63 for converting the pressure fluctuation or flow fluctuation of the air, jetted from the first nozzle 55, into a first measuring signal corresponding to the machined diameter of a measured part in the depth direction of a bore is disposed at the intermediate part of a first air passage 57 connecting the first air nozzle 55 to a first air source 61. A spindle 13 is provided with a detected body 71 with the tapered face 69 inclined in the depth direction. A second air nozzle 75 for jetting air to this tapered face 69 is provided at a fixed part 73, near the spindle 13. A second converter 79 for converting the pressure fluctuation or flow fluctuation of the air, jetted from the second air nozzle 75, into a second measuring signal corresponding to the depth position of a measured part is disposed at the intermediate part of a second air passage 77 connecting the second air nozzle 75 to a second air source 61.