signal input terminal of the 4 bit up down counter 3 thus the counter 3 which has been functioned as a down counter is changed to function as an up counter fig7 is a time chart showing a status of each signal in the pwm signal generating circuit 100 in a case in which the gradient setting value is set to u201c 00000100 u201d that is in a case in which an increasing rate of a luminescence duty ratio of the light emitting diode specified by the gradient setting value is set a relatively fast tempo fig8 is a time chart showing a status of each signal in the pwm signal generating circuit 100 in a case in which the gradient setting value is set to u201c 00011000 u201d that is in a case in which an increasing rate of the luminescence duty ratio of the light emitting diode specified by the gradient setting value is set to a relatively slow tempo as apparent from comparison between fig7 and fig8 by changing the gradient setting value a rate of increase and decrease of a period during which the pwm signal is at a high level within a cycle in which the set signal is output moreover as shown in fig7 and fig8 the flip flop 6 changes a signal level of the pwm signal to a high level in response to an input of the high level pulsed set signal output from the 4 bit counter section 1 as.