Most forms of decapitation have been performed by sharp and hanging rope. A 41-year-old man was found dead by decapitation on the roof of second story in the apartment where he lived. The separated head was placed apart from his torso. Each edge of the parts was relatively sharp. There were also a number of incised wounds in the face, neck, left arm, and abdomen. All wounds were accompanied with subcutaneous hemorrhage and hematoma, suggesting that these wounds had been performed during survival. The separated head was accompanied with the larynx, pharynx and the parts of lungs and heart. Severe recessus ran from his right shoulder to left lateral chest, which indicates that the victim’s chest was severely hit by the unsharp object such as the railing. Then the force of inertia was acted toward the head from the toe. The head attachments were pulled out by the gigantic force of inertia. The victim was injured several incised wounds on the neck and then received strong force to chest, which caused decapitation inducing death. The present case is the first report among decapitation. Force to the body causes decapitation as if wounds are injured by the sharp instrument.