a light emitting unit configured to emit a beam light for scan;

an image data supplying unit configured to process and supply image data of a target image in each line in a direction of main scan in response to a sync signal;

a delayed acquisition unit configured to acquire the image data supplied from the image data supplying unit after a certain time from generation of the sync signal; and

a control unit configured to control operation of the light emitting means by a driving signal which is generated based on the image data outputted from the delayed acquisition unit,

wherein the delayed acquisition unit comprises:

two first-in, first-out memory memories for separately storing the image data of odd-numbered pixels and even-numbered pixels in each line,

a writing unit configured to write the image data supplied from the image data supplying unit into the two memories in a manner separated into the odd-numbered pixels and the even-numbered pixels, and

a reading unit configured to read the image data written in the two memories after the certain time in a manner separated into the odd-numbered pixels and the even-numbered pixels, and

a combining unit configured to combine the image data of the odd-numbered pixels and the even-numbered pixels read by the reading unit into image data having the same order as an original data train,

wherein a frequency of a write data clock of the two memories is a half of a frequency of a data read clock of the two memories, and

wherein a writing pointer and a reading pointer of the two memories are cleared whenever one line has been formed in synchronism with the sync signal.