There are provided an image reader with high resolution capability for images in a high density range and an image forming apparatus. An image reader 2 comprises a reflected light reading unit (11, 12, 13, 14, 10) for irradiating a surface to be read of an original sheet with a light and reading the amount of the reflected light and a transmitted light reading unit (15, 12, 13, 14, 10) for irradiating the original sheet with a light and reading the amount of the transmitted light, and calculates the density of an image of the original sheet based on the amount of the reflected light read by the reflected light reading unit and the amount of the transmitted light read by the transmitted light reading unit.