A method for switching mode of a source device that uses a High Definition Multimedia Interface (HDMI) according to an embodiment of the present invention may include connecting to a sink device through the HDMI; transmitting +5V signal to the sink device; receiving a Hot Plug Detect (HPD) signal from the sink device; receiving EDID information including a first Sideband mode support information representing that the sink device supports a Sideband mode through a Display Data Channel (DDC) channel that operates in a DDC mode; transmitting a second Sideband mode support information representing that the source device supports a Sideband mode to the sink device; receiving instruction to perform an operation mode switching of the DDC channel from the sink device; and switching the operation mode of the DDC channel from the DDC mode to the Sideband mode.