  We observed the TeV blazar 1ES 1218+304 with the X-ray astronomy satellite
Suzaku in May 2006. At the beginning of the two-day continuous observation, we
detected a large flare in which the 5-10 keV flux changed by a factor of ~2 on
a timescale of 5x10^4 s. During the flare, the increase in the hard X-ray flux
clearly lagged behind that observed in the soft X-rays, with the maximum lag of
2.3x10^4 s observed between the 0.3-1 keV and 5-10 keV bands. Furthermore we
discovered that the temporal profile of the flare clearly changes with energy,
being more symmetric at higher energies. From the spectral fitting of
multi-wavelength data assuming a one-zone, homogeneous synchrotron self-Compton
model, we obtain B~0.047 G, emission region size R = 3.0x10^16 cm for an
appropriate beaming with a Doppler factor of delta = 20. This value of B is in
good agreement with an independent estimate through the model fit to the
observed time lag ascribing the energy-dependent variability to differential
acceleration timescale of relativistic electrons provided that the gyro-factor
\xi is 10^5.
