The present invention provides an image-forming device that can record an image onto a rewritable image recording medium. Prior to recording a predetermined image, the medium is set and a test image for measuring the density is recorded thereon. When the density is determined to be within an allowable range, the predetermined image is recorded under certain image recording conditions and then discharged to a discharging tray. However, should the density be outside the allowable range, the conditions are changed and another test image is recorded to the medium. If after repeated density measurements the density is not within an allowable range, the device determines that the medium is defective and discharges it to an error tray.