An image scanning apparatus includes three color line sensors for outputting red, green, and blue color signals, a monochrome line sensor for outputting a monochrome signal having a higher resolution than the color signals, and a resolution-enhancement processor. The resolution-enhancement processor enhances a resolution of a pixel signal of the color signals, based on a monochrome smoothed value obtained by smoothing a signal of an arbitrary pixel of the monochrome signal and signals of pixels around the arbitrary pixel and a color smoothed value obtained by smoothing a signal of a pixel of each color signal and signals of pixels around the pixel of the color signal, the pixel of the color signal corresponding to the position of the arbitrary pixel of the monochrome signal. The image scanning apparatus can perform high-luminance and high-resolution scanning with a 4-line configuration and can reduce color-misalignment phenomenon due to motor drive.