The IRAS Bright Galaxy Sample contains several moderate-luminosity galaxies
 exhibiting the similar IRAS spectra to those of "cool" ultraluminous infrared
 galaxies such as Arp 220 (e.g., NGC 2623). Namely, their infrared luminosities
 are less than 10^12 L(sun), and their IRAS spectra are nearly blackbody with
 color temperatures of 60-80 K (see Figure). These moderate-luminosity
 blackbody-like infrared galaxies (MBIGs) should be the early, dust-enshrouded
 stages in the evolution of Seyfert/starburst galaxies. This is because most of
 MBIGs are OH megamasers/absorbers, mergers, and/or show the enhanced ratios of
 the infrared luminosity to the molecular-gas mass. These are the properties
 characteristic of ultraluminous infrared galaxies, which are considered as the
 initial stages of quasars. Therefore, the studies of MBIGs will be essential to
 the complete understanding of Seyfert/starburst phenomena, as in the case of
 ultraluminous infrared galaxies being crucial to the study of quasars. However,
 the dominant energy sources of MBIGs are unknown. Hence we propose the PHOTO-S
 observation of MBIGs. The main purpose is the measurement of the PAH emission
 feature at 7.7 micron and the silicate absorption feature at 9.7 micron so as
 to determine the dominant energy sources (AGNs or OB stars). The PAH features
 are useful in estimating the contribution from OB stars to the far-infrared
 luminosity. This is because (1) the PAH features are excited by UV photons from
 OB stars, (2) the ratio of the number of the photons emitted in a certain PAH
 feature to the total number of absorbed UV/optical photons is constant, and (3)
 PAHs are destroyed by X-rays from AGNs. The 7.7 micron feature is stronger by a
 factor of 3-10 than the PAH features observable from the ground. Moreover, the
 reddening effect is very small at 7.7 micron. On the other hand, the depth of
 the silicate absorption feature is a measure of interstellar extinction. This
 kind of mid-infrared spectroscopy is available only with the advent of ISO. In
 particular, PHOTO-S is optimized for the investigations of PAH features and the
 9.7 micron absorption feature.