light on off drive control of the laser diode 11a as shown in fig2 the control means shown later 13 the notifying means 17 and the clear means 18 are constituted as software in the cpu 19 the control means 13 outputs the light on off command of the laser diode 11a to the ld lighting control unit 12a the timer unit time measuring means 14a is attached to the cpu 19 the timer unit 14a measures as a clock count value the time difference between the light on command output and the light off command output delivered from the control unit 13 to the ld lighting control means 12a or the period of lighting time of the laser diode 11a the ram storage means 15a stores the period of lighting time of the laser light source 11 measured by the timer unit 14a the ram 15a stores and holds temporarily the time count value measured by the timer unit 14a while the laser scanning device 24 is turned or powered off the cpu 19 transmits the data count value of the timer unit 14a to the ram 15a for storage immediately prior to the laser scanning device being turned off when the laser scanning device 24 is re.