the control unit 306 determines an amount of current being currently supplied to the disinfecting liquid dispenser 304 based on a magnitude of the converted voltage signal fig5 a 5e are charts showing waveforms of signals applied to the drive unit of fig4 as shown in fig5 a 5b the first and second switching signals 316 and 318 which are input signals have opposite phases respectively a slight dead time t d exists between transition points of the first and second switching signals 316 and 318 if the first and second switching signals 316 and 318 transition at a same time an overlapped range is formed in this case the two silver plates 220 and 222 of the disinfecting liquid dispenser 304 are short circuited when the dead time t d is provided between the first and second signals 316 and 318 the two silver plates 220 and 222 of the disinfecting liquid dispenser 304 can be prevented from short circuiting as shown in fig5 c the pulse width modulation signal 314 which is another input signal is a signal whose duty ratio is variable by the control unit 306 the duty ratio of the pulse width modulation signal 314 as shown in fig5 c is 100 as shown in fig5 d 5e the first and second control voltages 326 and 328 which are output signals have opposite phases a phase of the first control voltage 326 is a same phase as that of the first switching signal 316 while a phase of the second control voltage 328 is a same phase as that of the second switching signal 318 levels of the first and second control voltages 326 and 328 are proportional to the duty ratio of the pulse width modulation signal 318 in fig5 d 5e.