A slave device (20), which is a communication device, receives and analyzes commands, and returns the results to a master device (10). During the command analysis period, an IIC control unit (205) and a CPU (210), which form a control unit, control an SCL control unit (201) so as to stop an SCL signal. When the value of a timer (206) is equal to or less than a threshold value, transmit data are saved in a transmission FIFO (203), control for stopping the SCL signal is canceled, and in synchronization with the SCL signal, an SDA control unit (202) transmits the data saved in the transmission FIFO (203) to the master device (10). When the value of the timer (206) exceeds the threshold value, control for stopping the SCL signal is canceled, the clock control unit is placed in a state to receive the clock signal, and the SDA control unit (202) is placed in a state to receive a slave address indicating a communication device that operates in the slave mode.