1. An inspection apparatus which inspects a substrate comprising: an irradiating unit for irradiating inspection light on an inspection area of said substrate; a detecting unit for detecting scattered light from said substrate; a first processing unit which calculates a threshold value; a second processing unit which inspects a foreign matter of said substrate based on said threshold value; and a first display unit which displays a distribution image of said threshold value on said substrate, wherein said first processing unit calculates a standard deviation based on said inspection area, and calculates said threshold value by multiplying a coefficient by said standard deviation.