PURPOSE: To not only shorten a wait time, but also to eliminate the need to interpose firmware by detecting the rotating states of a laser source and a motor and deciding whether a device is ready to operate or not, and then starting the device.

CONSTITUTION: A power reset signal is inputted to counters 11 and 17 and an F.F. 12 simultaneously with the operation of the power switch of the device, thereby initializing respective circuits. Simultaneously, a spindle motor 35 which drives the laser source 1 and a polygon mirror 2 is actuated. When the output of the laser source 1 increases and the device becomes ready to operate, the output of a laser photosensor 5 also reaches a certain value and the output of an amplifier 6 becomes larger than a reference value cf, so that an output signal SINW is obtained from a comparator 7. When a spindle motor 35 which drives the polygon mirror 2 reaches a prescribed rotating speed, the signal coincides with the output signal WINDW of a decoder 14 all the time, so an output signal SINWO is inputted to the F.F. 12 and an OR circuit 13 from an AND circuit 10 at every specific period, so that a host device detects the operation ready state of the device.