A pattern generator generates test data to be transmitted. An encoding circuit generates amplitude data which represent a modulated signal waveform that corresponds to the test data. The amplitude data are generated in a parallel manner in the form of multiple amplitude data in increments of multiple sampling points set within a predetermined period for cycles of the predetermined period. A data rate setting unit receives the multiple amplitude data in increments of sampling points, latches the amplitude data at corresponding sampling timings, and sequentially outputs the amplitude data thus latched. A multi-level driver receives sequentially input amplitude data, and generates a test signal having a level that corresponds to the value of the amplitude data thus received.