An image forming apparatus, to which an external measurement device is connectable, including an image processor, a printer, a sensor arranged on a conveyance path, a controller that performs first processing for generating color processing condition based on a measurement result of measurement images of the sensor, the measurement images including a first measurement image and a second measurement image, wherein a length of the second measurement image in a conveyance direction is longer than a length of the first measurement image in the conveyance direction, and performs second processing for generating conversion condition, based on a measurement result of predetermined measurement images by the sensor and measurement data output from an external measurement device, wherein a length of a predetermined measurement image included in the predetermined measurement images in the conveyance direction is longer than the length of the first measurement image in the conveyance direction.