A main body portion is shaped in a cylinder and formed with an intake port which is a hole through which air from an outside flows into the cylinder. The main body portion has one end, which is provided with one-way valve to impede inflow of air from the outside, and the other end, which is not provided with the one-way valve and through which the subject breathes. The resistance setting unit variably sets a magnitude of an inflow resistance to air flowing into the main body portion. The pressure measurement unit measures a pressure of air moving in the cylinder of the main body portion as the intraoral pressure.
