We propose to extend spectrophotometry of M dwarf stars by PHOT-S with photometric calibration by PHOT-P to very late M dwarfs near the end of the main sequence. The purpose of our proposal is to clarify the infrared properties of very low mass stars (VLMSs) and establish the relationship of them to the basic physical properties of such stars. So far, little is known on the infrared spectra of M dwarfs (especially beyond 2.5 micron) because of their extreme faintness, but this knowledge should be very important to understand the atmospheric structure of M dwarfs and also as a basis of our future studies of brown dwarfs. We hope to obtain the infrared spectral energy distributions between 2.5 and 12 micron (except for a gap in 5-6 micron) by PHOT-S with photometric calibration by PHOT-P, and also extend the photometry to IRAS bands. The major scientific goals by our observations are: 1) To test the model atmospheres by comparing observed infrared flux with the predictions based on a new grid of model atmospheres of VLMSs covering the Teff range between 1,000 and 4,000K for the metallicities of the disk and halo (see Sect.4), and to determine the basic physical parameters of the atmospheres of M (sub)dwarfs. 2) To examine if there is any observational evidence such as silicate band at around 10 micron to show the dust formation in the dense and cool atmospheres of VLMSs. 3) To explore a possibility if an indication of the temperature inversion due to coronal heating can be found in the infrared where opacity is increasing due to the quasi-continuous absorption by the collision induced dipole transitions of H2 molecule and if this can resolve some known inconsistencies between observations and model predictions.