A Samisen is one of the typical plucked string instruments in traditional Japanese music. In this work, the sound generation mechanism of the Samisen will be discussed by analyzing how each part of the Samisen works. The Samisen sound is classified into four time regions by considering the characteristics of the waveform. The time--frequency analysis of the vibration waveform of each part in each time region is compared with that of the sound. Furthermore, the sound generation mechanism will be discussed, including the time region by the transient touch of the plectrum to the strings and the skin. It is concluded that both the cause of the vibration of the skin and the generation of the Samisen original sound are mainly due to two mechanisms: the transmission of the continuous vibration of strings through the bridge and the transient and direct touch of the plectrum.