PURPOSE: To provide side printing method and apparatus which is efficient and high in quality with a high accuracy by enabling exposing and printing contents such as characters, numerals, symbols and codes into a continuously moving film in instantaneous response to setting alteration according to the switching of size, type and the like.

CONSTITUTION: The titled side printing apparatus is composed of (A) a laser beam generator 1, (B) a laser beam modulator 4, (C) a laser beam deflector 7, (D) an image formation optical system comprising a reduction lens 3 and a image forming lens 6, (E) a position detector 10 for generating a signal proportional to the position of a moving photosensitive material 8, (F) a photo detector 11 for synchronization, (G) a character and mark setting device 12 for selecting the type of characters, numerals, symbols, codes and the like and (H) a main controller 5 for control said laser beam modulator outputting a signal for generating characters or the like receiving signals outputted from said position detector, said photo detector for synchronization and said mark setting device as input signal.