To open easily and safely a plastic bag by providing a plastic bag insertion opening in a part of an upright plate body and arranging slantly a blade along the opening in a cutter that cuts a plastic bag containing loaves, vegetables or the like that is sealed by a tape.

An insertion opening 1 is formed, extended diagonally downward, at the corner of the upper portion of a plate-form body A made of a synthetic resin standing upright vertically from a sill B1, a blade 2 is arranged in an inclined sate along this insertion opening 1. This blade 2 is fixed detachably by a blade stopper a4 and a blade stopper b5. A blade replacement lid 6 is arranged in the blade stopper a4 and fixed by tightening a screw 7. Therefore, by removing the blade replacement lid 6 by removing the screw 7 and drawing out, holding the edge of the blade 2 by fingers, the blade 2 can be taken out. Therefore, the blade 2 can be replaced easily. The edge of the insertion opening 1 opposite to the blade 2 is made a blade cover 8 and permits safe use.