A cutting method for crackly plate-shaped work piece and a cutting device thereof. The cutting method includes steps of: using a holding mold set to hold two faces of the crackly plate-shaped work piece along a predetermined cutting line and hold a product section of the crackly plate-shaped work piece that is to remain; and making a cutting mold move toward the crackly plate-shaped work piece by a stroke or up and down bite and cut the crackly plate-shaped work piece so as to cut off the crackly plate-shaped work piece along an edge of the holding mold set in alignment with the predetermined cutting line.