This paper describes an experiment to reveal the effect of the inner diameter of an artificial muscle on the instantaneous force generation mechanism based on the striking motion of the mantis shrimp. The purpose of this study is to construct a method for the design of a mechanism inspired by the striking motion of organisms that move faster than its muscle contraction using the mechanisms of the elastic elements of its exoskeleton. In previous studies, we revealed the effect of increasing speed and striking force by the elastic elements of the exoskeleton using both the model and the developed mechanism. However, the effect of the contraction characteristics of the artificial muscle was not clearly indicated because the experiment in the previous studies only focused on the elastic elements of the exoskeleton. Therefore, it was difficult to comprehensively design the mechanism, including the characteristics of the artificial muscles. Hence, the aim of this study is to reveal the effect of the characteristic change of the artificial muscle using different parameters of the artificial muscle. For this, the time to hit and the hitting speeds were measured for the developed mechanism incorporating the artificial muscle with three different inner diameters (11 mm, 13 mm, and 15 mm). The developed mechanism showed the fastest time and speed (0.208 s and 2.28 m/s, respectively) when the artificial muscle diameter was 15 mm.