An image forming apparatus capable of detecting a development nip disengaging error, the image forming apparatus comprising: a photoconductor ; a charging device to apply a charging voltage to charge the photoconductor ; an exposing device to expose the photoconductor to light to form an electrostatic latent image thereon; a developing roller to supply toner to the electrostatic latent image formed on the photoconductor and develop a toner image; an adjusting member to move the developing roller to a developing position where the developing roller is in contact with the photoconductor to form a development nip (N) and to a disengaging position where the developing roller is spaced apart from the photoconductor and the developing nip (N) is disengaged from the photoconductor ; an intermediate transfer belt to receive the toner image formed on the photoconductor ; a sensor to detect the toner image transferred to the intermediate transfer belt ; and a control unit to: form a test pattern on the photoconductor , detect the test pattern transferred to the intermediate transfer belt through the sensor from a time when an operation of the adjusting member is controlled so as to move the developing roller from the disengaging position to the developing position, and determine whether the development nip disengaging error occurred according to a length of the test pattern transferred to the intermediate transfer belt in a moving direction of the intermediate transfer belt . a photoconductor ; a charging device to apply a charging voltage to charge the photoconductor ; an exposing device to expose the photoconductor to light to form an electrostatic latent image thereon; a developing roller to supply toner to the electrostatic latent image formed on the photoconductor and develop a toner image; an adjusting member to move the developing roller to a developing position where the developing roller is in contact with the photoconductor to form a development nip (N) and to a disengaging position where the developing roller is spaced apart from the photoconductor and the developing nip (N) is disengaged from the photoconductor ; an intermediate transfer belt to receive the toner image formed on the photoconductor ; a sensor to detect the toner image transferred to the intermediate transfer belt ; and a control unit to: form a test pattern on the photoconductor , detect the test pattern transferred to the intermediate transfer belt through the sensor from a time when an operation of the adjusting member is controlled so as to move the developing roller from the disengaging position to the developing position, and determine whether the development nip disengaging error occurred according to a length of the test pattern transferred to the intermediate transfer belt in a moving direction of the intermediate transfer belt . form a test pattern on the photoconductor , detect the test pattern transferred to the intermediate transfer belt through the sensor from a time when an operation of the adjusting member is controlled so as to move the developing roller from the disengaging position to the developing position, and determine whether the development nip disengaging error occurred according to a length of the test pattern transferred to the intermediate transfer belt in a moving direction of the intermediate transfer belt . <EOS>