An image forming apparatus comprising: an image forming means (120-123) configured to form a plurality of measurement images including a first measurement image and a second measurement image_on a sheet; a conveyance means configured to convey the sheet; a measurement means configured to measure the plurality of measurement images by accumulating reflected light from the plurality of measurement images on the sheet conveyed by the conveyance means; a control means configured to: control the image forming means to form the plurality of measurement images on the sheet, cause the conveyance means to convey the sheet toward the measurement means, control the measurement means to execute a first scan in which the measurement means measures each of the plurality of measurement images, cause the conveyance means to convey the sheet once again toward the measurement means, and control the measurement means to execute a second scan in which the measurement means measures the each of the plurality of measurement images; and a determination means configured to: determine a first reflected light accumulation time during which the measurement means accumulates reflected light from the first measurement image in the second scan, based on a measurement result of the first measurement image by the measurement means in the first scan, and determine a second reflected light accumulation time during which the measurement means accumulates reflected light from the second measurement image in the second scan, based on a measurement result of the second measurement image by the measurement means in the first scan. control the image forming means to form the plurality of measurement images on the sheet, cause the conveyance means to convey the sheet toward the measurement means, control the measurement means to execute a first scan in which the measurement means measures each of the plurality of measurement images, cause the conveyance means to convey the sheet once again toward the measurement means, and control the measurement means to execute a second scan in which the measurement means measures the each of the plurality of measurement images; and a determination means configured to: determine a first reflected light accumulation time during which the measurement means accumulates reflected light from the first measurement image in the second scan, based on a measurement result of the first measurement image by the measurement means in the first scan, and determine a second reflected light accumulation time during which the measurement means accumulates reflected light from the second measurement image in the second scan, based on a measurement result of the second measurement image by the measurement means in the first scan. determine a first reflected light accumulation time during which the measurement means accumulates reflected light from the first measurement image in the second scan, based on a measurement result of the first measurement image by the measurement means in the first scan, and determine a second reflected light accumulation time during which the measurement means accumulates reflected light from the second measurement image in the second scan, based on a measurement result of the second measurement image by the measurement means in the first scan. <EOS>