In a laser exposure device according to the present invention, a positioning pin, which is formed in a lens holder supporting a lens system, is inserted through an elongated hole for restriction of a board holder supporting a laser diode. An eccentric cam is inserted into an elongated hole for rotation movement formed in a board holder and a circular hole for rotation movement which is formed in the lens holder and which faces the elongated hole for rotation movement. An eccentric cam is inserted into an elongated hole for slide movement formed in the board holder and a circular hole for slide movement which is formed in the lens holder and which faces the elongated hole for slide movement. The eccentric cams are rotated to relatively move the board holder and lens holder with respect to each other to thereby establish alignment between the optical axes of the laser diode and lens system. In a state where the eccentric cams are fitted into the elongated holes, the board holder and lens holder are fixed to each other by screws.