  We calculate the specific heat of composite fermion system in the half-filled
Landau level. Two different methods are used to examine validity of the
quasiparticle approximation when the two-body interaction is given by $V(q) =
V_0 / q^{2-\eta}$ ($1 \le \eta \le 2$). The singular part of the specific heat
is calculated from the free energy of the gauge field, which is compared with
the specific heat calculated from the quasiparticle approximation via the
singular self-energy correction due to the gauge field fluctuations. It turns
out that two results are in general different and they coincide only for the
case of the Coulomb interaction ($\eta = 1$). This result supports the fact
that the quasiparticle approximation is valid only for the case of the Coulomb
interaction. It is emphasized that this result is obtained by looking at a
gauge-invariant quantity -- the specific heat.
