An image inspection apparatus includes: a light source configured to emit white light onto a test image formed on a paper sheet; an optical lens system configured to receive light reflected by the paper sheet, the reflected light being of the white light emitted from the light source; a separating unit configured to separate light having passed through the optical lens system; a reading unit configured to receive the separated light at the different wavelengths, and optically read the test image of the light; and a control unit configured to calculate edge blurs at a rising edge and a falling edge of each set of image data of the light obtained by the reading unit reading the test image, calculate widths of the test image, and determine the width calculated from the set of image data having the smallest edge blur to be the width of the test image.