In a first output mode, a signal in which a data pulse having a positive polarity voltage value appears in a predetermined cycle is output as a positive polarity gradation data signal, and a signal in which a data pulse having a negative polarity voltage value appears in the predetermined cycle with a phase different from the positive polarity gradation data signal is output as a negative polarity gradation data signal. In a second output mode, the above positive polarity gradation data signal is generated, and a signal in which a data pulse having a negative polarity voltage value appears in the predetermined cycle with the same phase as the positive polarity gradation data signal is output as the negative polarity gradation data signal. The first and second output modes are alternatively executed, and the output mode is switched within a predetermined period at intervals of the predetermined period.