  We studied a time history of X-ray spectral states of a black-hole candidate,
4U 1630-47, utilizing data from a number of monitoring observations with the
Rossi X-Ray Timing Explorer over 1996--2004. These observations covered five
outbursts of 4U 1630-47, and most of the data recorded typical features of the
high/soft states. We found that the spectra in the high/soft states can be
further classified into three states. The first spectral state is explained by
a concept of the standard accretion disk picture. The second state appears in
the so-called very high state, where a dominant hard component is seen and the
disk radius apparently becomes too small. These phenomena are explained by the
effect of inverse Compton scattering of disk photons, as shown by Kubota,
Makishima, & Ebisawa (2001, ApJ, 560, L147) for GRO J1655-40. The third state
is characterized in such a way that the disk luminosity varies in proportion to
$T_{\rm in}^2$, rather than $T_{\rm in}^4$, where $T_{\rm in}$ is the
inner-disk temperature. This state is suggested to be an optically-thick and
advection-dominated slim disk, as suggested by Kubota & Makishima (2004, ApJ,
601, 428) for XTE J1550-564. The second and third states appear, with good
reproducibility, when $T_{\rm in}$ and the total X-ray luminosity are higher
than 1.2 keV and $\sim2.5\times10^{38}(D/10\quad{\rm kpc})^2\l
eft[\cos{\theta}/(1/\sqrt{3})]^{-1}$ erg s$^{-1}$, respectively, where $D$ is
the distance to the object and $\theta$ is the inclination angle to the disk.
The present results suggest that these three spectral states commonly appear
among black-hole binaries under high accretion rates.
