Provided are a testing device and a testing method which reduce circuit size. A reproduction clock generating circuit for generating a reproduction clock approximately equal to the phase of output data outputted by a device under test is provided with a phase comparator for comparing the phase of the output data outputted by the device under test with the phase of the reproduction clock and outputting a phase difference signal, a binary counter, the output value of which increases or decreases according to the phase difference signal, a control signal generating section for generating a control signal according to the output value of the binary counter, and a phase shifter for shifting the phase of the reference clock according to the control signal.