PURPOSE: To process character data into a digital video signal with fidelity by eliminating the digital video signal in a superimposition circuit when the character data generated from a character generator circuit are processed into the digital video signal.

CONSTITUTION: The processing unit is provided with an oscillator 11 generating a clock signal being a reference signal of a signal processing circuit, a character generator circuit 12 using a clock signal from the oscillator 11 as a reference signal and generating the character data from a vertical synchronizing signal and a horizontal synchronizing signal and a superimposition circuit 13 converting the character data outputted from the character generator circuit 12 into a digital video signal and superimposing the digital video signal onto the input digital video signal and providing the superimposed output digital video signal, a vertical synchronizing signal and a horizontal synchronizing signal synchronously with the output digital video signal.