1. An image forming apparatus comprising: a fixing roller configured to be able to rotate in contact with a printing medium while being heated by a heating device and contact and heat a toner image formed on the printing medium so as to weld the toner image to the printing medium; a motor configured to supply a rotational force to the fixing roller; and a motor driver configured to receive a drive voltage supplied from a direct-current power supply and control drive of the motor by the drive voltage; a cover member configured to be able to change a position thereof between an open position to open an opening formed in a housing of the image forming apparatus and a closed position to close the opening, and be opened or closed when a printing medium that has stopped in contact with the fixing roller is removed; characterised by further comprising: a cover switch including a contact whose one end is connected to the direct-current power supply and another end is connected to the motor driver, and configured to output an open signal corresponding to the open position and a close signal corresponding to the closed position, and power off the motor by opening the contact when the cover member is at the open position; a rotation signal detection portion connected to a voltage supply path which extends from the cover switch to the motor driver, and configured to detect, as a rotation signal indicating that the fixing roller is rotated, a counter electromotive force generated from the motor as a result of the fixing roller being rotated while the motor is being powered off by the cover switch; and a control portion connected to the cover switch in such a way that the open signal and the close signal can be input, and connected to the rotation signal detection portion in such a way that the rotation signal can be input, and configured to, when the rotation signal is input from the rotation signal detection portion while the open signal has been input from the cover switch, and then the close signal is input from the cover switch,_determine that the printing medium that has stopped in contact with the fixing roller is removed. a fixing roller configured to be able to rotate in contact with a printing medium while being heated by a heating device and contact and heat a toner image formed on the printing medium so as to weld the toner image to the printing medium; a motor configured to supply a rotational force to the fixing roller; and a motor driver configured to receive a drive voltage supplied from a direct-current power supply and control drive of the motor by the drive voltage; a cover member configured to be able to change a position thereof between an open position to open an opening formed in a housing of the image forming apparatus and a closed position to close the opening, and be opened or closed when a printing medium that has stopped in contact with the fixing roller is removed; characterised by further comprising: a cover switch including a contact whose one end is connected to the direct-current power supply and another end is connected to the motor driver, and configured to output an open signal corresponding to the open position and a close signal corresponding to the closed position, and power off the motor by opening the contact when the cover member is at the open position; a rotation signal detection portion connected to a voltage supply path which extends from the cover switch to the motor driver, and configured to detect, as a rotation signal indicating that the fixing roller is rotated, a counter electromotive force generated from the motor as a result of the fixing roller being rotated while the motor is being powered off by the cover switch; and a control portion connected to the cover switch in such a way that the open signal and the close signal can be input, and connected to the rotation signal detection portion in such a way that the rotation signal can be input, and configured to, when the rotation signal is input from the rotation signal detection portion while the open signal has been input from the cover switch, and then the close signal is input from the cover switch,_determine that the printing medium that has stopped in contact with the fixing roller is removed. a cover switch including a contact whose one end is connected to the direct-current power supply and another end is connected to the motor driver, and configured to output an open signal corresponding to the open position and a close signal corresponding to the closed position, and power off the motor by opening the contact when the cover member is at the open position; a rotation signal detection portion connected to a voltage supply path which extends from the cover switch to the motor driver, and configured to detect, as a rotation signal indicating that the fixing roller is rotated, a counter electromotive force generated from the motor as a result of the fixing roller being rotated while the motor is being powered off by the cover switch; and a control portion connected to the cover switch in such a way that the open signal and the close signal can be input, and connected to the rotation signal detection portion in such a way that the rotation signal can be input, and configured to, when the rotation signal is input from the rotation signal detection portion while the open signal has been input from the cover switch, and then the close signal is input from the cover switch,_determine that the printing medium that has stopped in contact with the fixing roller is removed.