  We report results from the X-ray and optical monitoring of the black hole
candidate MAXI J1820+070 (=ASSASN-18ey) over the entire period of its outburst
from March to October 2018.In this outburst, the source exhibited two sets of
`fast rise and slow decay'-type long-term flux variations. We found that the
1--100 keV luminosities at two peaks were almost the same, although a
significant spectral softening was only seen in the second flux rise. This
confirms that the state transition from the low/hard state to the high/soft
state is not determined by the mass accretion rate alone. The X-ray spectrum
was reproduced with the disk blackbody emission and its Comptonization, and the
long-term spectral variations seen in this outburst were consistent with a disk
truncation model. The Comptonization component, with a photon index of 1.5-1.9
and electron temperature of ~>40 keV, was dominant during the low/hard state
periods, and its contribution rapidly decreased (increased) during the spectral
softening (hardening). During the high/soft state period, in which the X-ray
spectrum became dominated by the disk blackbody component, the inner disk
radius was almost constant, suggesting that the standard disk was present down
to the inner most stable circular orbit. The long-term evolution of optical and
X-ray luminosities and their correlation suggest that the jets substantially
contributed to the optical emission in the low/hard state, while they are
quenched and the outer disk emission dominated the optical flux in the
intermediate state and the high/soft state.
