PURPOSE: To allow an enlarged frame to constantly follow so as to eliminate the delay according to displacement by impressing a pulse having a predetermined pulse width as a driving signal, and by impressing a pulse having a width longer than the predetermined pulse width relative to a last on-signal of a series of on-signals before a first off-signal starts.

CONSTITUTION: In a case where current output data are on, while output data next thereto are off, when a driving signal having a pulse T2 is supplied to a driver 15 from CPU 13, the driver 15 supplies to a head 16 a driving voltage corresponding to the voltage signal, whereby in a case where there appears an OFF in the output data after the output voltage continues to be on, it is possible to make an enlarged frame follow by impressing a driving signal having a pulse width T2 longer than a pulse width T1 relative to the last on-signal. Although the above describes a case where there appears an OFF in output data after the output voltage continues to be on, this will also be true with a case where there appears an OFF in the output data after the initial output voltage becomes on.