PURPOSE: To improve a display grade by using a signal converted to AC of the frequency higher than a frame frequency and different from the factor of a duty to drive a liquid crystal.

CONSTITUTION: Signals Vb', Va' are made substantially equal in the effective value and the contrasts of dots (b), (a) are substantially equal if the signal M' converted to the AC of the higher frequency inverted at every 2 shots of a clock CL, rather than the signal M converted to the AC inverted at every one frame is used. The negative side of the signal Vb' turns to the positive side in some cases according to display patterns upon incoming of the on signal synchronized with the inversion of the signal M' and eventually an uneven display arises. Such uneven display is eliminated if the signal M' in which ≥2 kinds of the frequencies mixedly exist is used. The signal M' which inverts at every 12 shots of the clock CL and inverts at every 16 shots is generated in a circuit for generating the signal M'. The uneven display is thereby eliminated and the display grade is improved.