In the present study, the effect of the specimen size on the vibrational wave superimposed on the load-deflection curve of polymers is first investigated. Next, in the instrumented Charpy test, a shock-absorbing material is used in order to prevent the generation of the vibrational wave superimposed on the load-deflection curve, and its validity is discussed. Further, differences of the impact response curves obtained by an instrumented Charpy test and the one-point bend test are compared and discussed. The results of this study are summarized as follows. (1) The vibrational wave can be prevented by using a small specimen which shortens the period of the vibrational wave. (2) The load value is lowered by using shock-absorbing material. (3) The differences in the impact response curves and the fracture times obtained from the instrumented Charpy impact test and the one-point bend test are rather large in the lower impact velocity of 3.10m/s; however, the obtained K_Id values are nearly coincidental.