M supergiant stars are among the most luminous stars in the Galaxy
 and are therefore of interest to study both the galactic structure
 and the evolution of our Galaxy.  Most M supergiants lose their
 masses and dust formation takes place around them.  Since these
 stars emit much energy in the infrared via these dust grains, it
 is important to make clear the properties of these dust grains.
 Infrared excesses of M supergiants has been characterized by the
 silicate dust emission and the free-free emission which is not
 seen around less massive cool evolved stars.  However, recent mid-
 infrared observations show that carbon dust features are also seen
 around several M supergiants together with silicate one,
 suggesting an occurrence of complicated non-equilibrium
 condensation.

 We propose here to take systematically infrared spectra of M
 supergiants using SWS (SWS01).  Our main objectives of this study
 are to make clear the properties of dust grains and to investigate
 the formation of dust grains around M supergiants.  The obtained
 spectra are also useful to understand the atmospheric structure of
 these stars.  Furthermore, the results are used to estimate the
 mass loss rates and the chemical abundances of heavy elements and
 to give information on the mass loss phenomenon and its effect on
 stellar evolution.  All these will give us useful data to
 investigate the galactic structure and the evolution of the
 Galaxy.