an HS (High Speed) driver as a transmission circuit in an HS mode of USB (Universal Serial Bus);

an amplitude detection circuit configured to detect a signal amplitude of a USB signal;

an amplitude setting circuit configured to set an amplitude setting value of the signal amplitude of the USB signal; and

a judgment circuit, wherein the amplitude setting circuit varies the signal amplitude with the amplitude setting value in a detection period, and the judgment circuit determines the amplitude setting value to be used by the amplitude setting circuit when performing HS communication based on a detection result by the amplitude detection circuit in the detection period,

wherein the amplitude detection circuit is directly electrically connected to the HS driver to measure the detection result,

the HS driver includes a current source configured to output a variable transmission current, and the amplitude setting circuit sets a value of the transmission current as the amplitude setting value to thereby set the signal amplitude by outputting an instruction signal for setting the value of the transmission current to the current source and the current source increases the value of the transmission current, and

wherein the judgment circuit varies the signal amplitude after a termination resistor is set ON.