Abstract: A package opening cutter is provided which can accurately, safely and efficiently open the package without damaging the merchandise inside and in which the cutter will not come out during use. It comprises an angle ruler, retaining portions provided at both sides of the angle ruler, a clamp body provided so as to be pushed into and pulled out of the retaining portion for clamping a cutter, and an arrangement for preventing the clamp body from coming out of the retaining portion. The arrangement for preventing the clamp body from coming out has a bolt slidably provided between the cutter retaining portions and the cutter clamp body. The bolt is operated by a knob provided on an outer surface of the cutter retaining portion.