Secondary ion mass spectrometry (SIMS) has become useful in the fields of geo-and cosmo-sciences as well as other various fields of industries, medicine, pharmacy, biology, etc. In geo-and cosmo-sciences, one of the merits of in situ isotopic analysis of SIMS is particularly significant. Applications of SIMS to diffusion study, age determination, investigation of isotopic anomaly are briefly reviewed. A development of a new SIMS with high mass resolution which is now proceeding in Naruto University of Education is described in section 5.