A converter device supplied with a drive power from an image forming apparatus instead of an external device and an image forming apparatus connected to the converter device. The converter device is provided between the image forming apparatus including a power supply port and a USB port and a host device including a parallel port such that data is transmitted and received between the image forming apparatus and the host device. The converter device is connected to the image forming apparatus through the power supply port and a power cable to be supplied with power. The converter device is operated with the supplied power to convert data output from the USB port into data capable of being input to the parallel port or convert data output from the parallel port into data capable of being input to the USB port.