  We present the results of the simultaneous observation of the giant radio
pulses (GRPs) from the Crab pulsar at 0.3, 1.6, 2.2, 6.7, and 8.4 GHz with four
telescopes in Japan. We obtain 3194 and 272 GRPs occurring at the main pulse
and the interpulse phases, respectively. A few GRPs detected at both 0.3 and
8.4 GHz are the most wide-band samples ever reported. In the frequency range
from 0.3 to 2.2 GHz, we find that about 70\% or more of the GRP spectra are
consistent with single power laws and the spectral indices of them are
distributed from $-4$ to $-1$. We also find that a significant number of GRPs
have such a hard spectral index (approximately $-1$) that the fluence at 0.3
GHz is below the detection limit ("dim-hard" GRPs). Stacking light curves of
such dim-hard GRPs at 0.3 GHz, we detect consistent enhancement compared to the
off-GRP light curve. Our samples show apparent correlations between the
fluences and the spectral hardness, which indicates that more energetic GRPs
tend to show softer spectra. Our comprehensive studies on the GRP spectra are
useful materials to verify the GRP model of fast radio bursts in future
observations.
