PROBLEM TO BE SOLVED: To provide a method and an apparatus for treatment of corner parts of a skin material which enable an automatic folding treatment of corner parts of a skin material in a skin-provided molding.SOLUTION: A method of treating corner parts of a skin material includes a step of pushing in a corner part 3c of a skin material in an erected state toward the central side of a mold by means of tip arc parts 11b of a pair of right and left slide plates 11 sliding-movable toward the center of the die on the end surface of a female die and bending toward the back surface of the slide plates 11 while gathering toward the mating surface of the slide plates along the tip art parts 11b, a step of causing the slide plates 11 advance further and guiding to a hole part 20 on the rear side in a state where the central part of the surface of the bent corner part 3c of the skin material is allowed to escape outward from a passage 21 formed at the tip of the slide plates 11, a step of inserting a pressing membe
