1. A method of inspecting a phase-shifting mask used in an exposure step of a process of manufacturing a semiconductor device, comprising the steps of: (a) producing first pattern data as a function of a given circuit pattern; (b) converting said first pattern data into second pattern data used for manufacturing a phase-shifting mask; (c) manufacturing said phase-shifting mask as a function of said second pattern data; (d) detecting a pattern of said phase-shifting mask using optical conditions related with those of said exposure step which makes use of a phase shift method to obtain image data; and (e) checking said image data with said first pattern data; wherein said step of detecting a pattern of said phase-shifting mask is performed using a mask detector and comprises: projecting single-wavelength light using a light source; introducing said light from said light source onto a mask surface of said phase-shifting mask using a first optical system; forming an optical image of said light which passes through said phase-shifting mask using a second optical system; imaging said optical image of said phase-shifting mask to obtain image data using an imaging means; and setting said mask detector to satisfy the following relations, EQU .lambda.1=.lambda. EQU .sigma.1=.sigma. EQU m1.multidot.A1=m.multidot.A EQU m1&gt;m where A1 and m1 represent a numerical aperture and a magnification of said mask detector, .lambda.1 and .sigma.1 represent a wavelength and a coherence of said light projected from said light source respectively, while A and m represent a numerical aperture and a magnification of said exposure device used in a process of manufacturing a semiconductor device, .lambda. and .sigma. represent a wavelength and a coherence of light used therein; said method further comprising inspecting with an enlarged pattern based on EQU R1=(m1/m).multidot.R; where R1 and R represent minimum resolving powers of said mask detector and said exposure device used in a process of manufacturing a semiconductor device, respectively.