Inspection apparatus and adjusting method

An inspection apparatus which can be accurately calibrated regardless of a use environment or an amount of use time is implemented. A reference substrate 100 provided with a diffraction grating 107 is mounted on a transport system 110, an illumination region 106 is formed on the diffraction grating 107 by light 105 from an illumination optical system 104, reflected light is collected by a detection optical system 108, and an output value from a sensor 111 is measured. It is determined whether or not a difference between a simulation value preserved in a processing section 112 and the output value from the sensor 111 is within a predetermined allowable range, and the optical system is adjusted so that the difference enters the allowable range. Since standard data for performing calibration on the inspection apparatus is obtained by using the diffraction grating, it is possible to implement the inspection apparatus which can be accurately calibrated regardless of a use environment or an amount of use time.