An image forming apparatus comprising: an image forming means (106, 120, 121, 122, 123) for forming a measurement image on a sheet; a measurement means for irradiating the measurement image with light and measure light reflected from the measurement image; a white reference plate arranged to be movable to a first position opposed to the measurement means and a second position separated farther from the measurement means than the first position; a shielding means arranged to be movable to a third position where the shielding means blocks the light with which the measurement means irradiates the white reference plate and a fourth position where the shielding means does not block the light; a conveyance means arranged to be movable to a fifth position opposed to the measurement means, a sixth position separated farther from the measurement means than the fifth position and a seventh position between the fifth and sixth positions, and to convey the sheet; and a control means for controlling positions of the white reference plate, the shielding means and the conveyance means, and characterised in that when the measurement means measures the white reference plate, the control means is configured to: move the shielding means to the fourth position, move the white reference plate to the first position, and move the conveyance means to the sixth position; when the measurement means measures the measurement image, the control means is configured to: move the shielding means to the third position, move the white reference plate to the second position, and move the conveyance means to the fifth position; and when in a print operation not including measurement by the measurement means, the control means is configured to: move the shielding means to the third position, move the white reference plate to the second position, and move the conveyance means to the seventh position. an image forming means (106, 120, 121, 122, 123) for forming a measurement image on a sheet; a measurement means for irradiating the measurement image with light and measure light reflected from the measurement image; a white reference plate arranged to be movable to a first position opposed to the measurement means and a second position separated farther from the measurement means than the first position; a shielding means arranged to be movable to a third position where the shielding means blocks the light with which the measurement means irradiates the white reference plate and a fourth position where the shielding means does not block the light; a conveyance means arranged to be movable to a fifth position opposed to the measurement means, a sixth position separated farther from the measurement means than the fifth position and a seventh position between the fifth and sixth positions, and to convey the sheet; and a control means for controlling positions of the white reference plate, the shielding means and the conveyance means, and move the shielding means to the fourth position, move the white reference plate to the first position, and move the conveyance means to the sixth position; move the shielding means to the third position, move the white reference plate to the second position, and move the conveyance means to the fifth position; and move the shielding means to the third position, move the white reference plate to the second position, and move the conveyance means to the seventh position.