Abstract: A method of manufacturing a laser irradiation device for oral treatment includes (a) molding a base frame having a tongue fixing frame part convexly formed upward so that the tongue is inserted into a lower space thereof and a teeth seating part concavely formed so that human teeth are seated therein, (b) assembling an LED strip with respect to the base frame, the LED strip having a plurality of laser diodes installed on a flexible circuit board to correspond to the shape of the base frame, (c) injecting a liquid light-transparent resin material into an upper light-transparent cover and a lower light-transparent cover respectively corresponding to the shapes of upper and lower parts of the base frame, and (d) respectively pressing the upper light-transparent cover and the lower light-transparent cover vertically upward and downward with respect to the base frame.