An interface device, used in a host device connected to a slave device to transmit and receive data and/or a command to and from the slave device, that switches an interface voltage used for communication between the slave device and the host device, the interface device comprising: a clock output unit that outputs a clock signal for transmitting and receiving the data and/or the command; a terminal group including one or more input/output terminal units that transmits and receives the data and/or the command using one of a first interface voltage and a second interface voltage; and an interface voltage switching unit that selects one of the first interface voltage and the second interface voltage and switches the interface voltage used for communication between the host device and the slave device to the selected one of the first and second interface voltages, wherein the interface voltage switching unit includes a control unit, a clock control unit that is controlled by the control unit, the clock control unit fixes a level of a signal output from the clock output unit to a first signal level when the interface voltage used for communication between the host device and the slave device is to be switched, and, when an interface voltage in the host device has been switched to the selected interface voltage, controls the clock output unit to output a clock signal using the selected interface voltage, and an input/output terminal control unit controlled by the control unit, the input/output terminal control unit sets the one or more input/output terminal units to an input state, monitors a level of an input signal into the one or more input/output terminal units when the interface voltage used for communication between the host device and the slave device is to be switched, and, when detecting that the level of the input signal Into the one or more input/output terminal units becomes a signal level indicating that an interface voltage in the slave device has been switched to the selected interface voltage, transmits a notification indicating the detection result to the control unit, and the control unit determines that the interface voltage in the slave device has been switched when receiving the notification indicating that the interface voltage switching has been completed in the slave device transmitted from the input/output terminal control unit after the clock control unit is set to a state in which the clock signal is being outputted using the selected interface voltage. a clock output unit that outputs a clock signal for transmitting and receiving the data and/or the command; a terminal group including one or more input/output terminal units that transmits and receives the data and/or the command using one of a first interface voltage and a second interface voltage; and an interface voltage switching unit that selects one of the first interface voltage and the second interface voltage and switches the interface voltage used for communication between the host device and the slave device to the selected one of the first and second interface voltages, wherein the interface voltage switching unit includes a control unit, a clock control unit that is controlled by the control unit, the clock control unit fixes a level of a signal output from the clock output unit to a first signal level when the interface voltage used for communication between the host device and the slave device is to be switched, and, when an interface voltage in the host device has been switched to the selected interface voltage, controls the clock output unit to output a clock signal using the selected interface voltage, and an input/output terminal control unit controlled by the control unit, the input/output terminal control unit sets the one or more input/output terminal units to an input state, monitors a level of an input signal into the one or more input/output terminal units when the interface voltage used for communication between the host device and the slave device is to be switched, and, when detecting that the level of the input signal Into the one or more input/output terminal units becomes a signal level indicating that an interface voltage in the slave device has been switched to the selected interface voltage, transmits a notification indicating the detection result to the control unit, and the control unit determines that the interface voltage in the slave device has been switched when receiving the notification indicating that the interface voltage switching has been completed in the slave device transmitted from the input/output terminal control unit after the clock control unit is set to a state in which the clock signal is being outputted using the selected interface voltage.