A pattern inspection apparatus includes a magnification conversion unit to convert first sample optical image data to higher resolution second sample optical image data, a low-pass filter configured to filter first design image data which has a resolution N times that of the first sample optical image data, an optical filter which calculates third design image data by convolving the second design image data with an optical model function, a coefficient acquisition unit configured to acquire a coefficient of the predetermined optical model function using the second sample optical image data and the third design image data, an optical image acquisition unit configured to acquire actual optical image data of an inspection target workpiece, a reference image data generation unit configured to generate reference image data corresponding to the actual optical image data, and a comparison unit configured to compare the actual optical image data with the reference image data.