By limiting a current change rate of a power to be supplied to a peltier element by using a pulse width control means for controlling to increase/decrease a pulse width of a pulse signal so that a temperature change of the peltier element does not exceed a predetermined temperature gradient and a switching means for controlling to turn on/off a drive current to be supplied to the peltier element based on a pulse signal having a pulse width controlled by the pulse width control means, an abrupt change of a rate of expansion and a rate of shrinkage of respective parts of the peltier element are suppressed and a stress imposed to the peltier element can be reduced, consequently, a lifetime of the peltier element can be maintained long.