This paper describes design of user interface and algorithm for selecting target fundamental tones in order to develop an assist device for tuning of shamisen. The sound of shamisen has a feature that harmonics is greater than fundamental and contains non-integer harmonics. It is difficult for beginners to tune a target tone of shamisen in lessons. Usability tests are carried out to determine the adequate user interface for tuning process of shamisen. The algorithm for selecting fundamental tones of shamisen is also proposed and mounted in one chip microcomputer. A prototype assist device for tuning of shamisen is developed and manufactured. As a result of verification by the prototype device of the shamisen tuner, it is possible for beginners to support to tune the fundamental tone of the shamisen.