  The effect of the strange quark in the finite temperature phase transition of
QCD is studied on the lattice. Using the one-plaquette gauge action and the
Wilson quark action, the transition in the chiral limit is shown to be
continuous for the case of degenerate two flavors, $N_F=2$, while it is of
first order for $N_F \geq 3$. For a more realistic case of massless up and down
quarks and a light strange quark, $N_F=2+1$, clear two state signals are
observed both for $m_s \simeq 150$ and 400 MeV. In contrast to a previous
result with staggered quarks, this suggests a first order transition in the
real world. In order to see the implication of these results to the continuum
limit, we started to study these issues using improved actions. First results
using a RG improved gauge action combined with the standard Wilson quark is
presented for the case of $N_F=2$: With this action the finite temperature
transition is shown to be continuous in the chiral limit confirming the result
of the standard action. Furthermore, not like the case of the standard action
where lattice artifacts make the transition once very strong at intermediate
values of the hopping parameter $K$ on $N_t=4$ and 6 lattices, a smooth
crossover is found for the improved action when we increase $1/K-1/K_c$, in
accord with a naive expectation about the fate of second order chiral
transition at finite $m_q$.
