  We discuss what we can understand from $\phi_1$ and $B^0_d\to \pi^+ \pi^- $
decay mode. Using a convention without weak phases $\phi_2$ and $\phi_3$, we
can solve the parameters from the time-depended CP asymmetry. If we can put a
condition the contribution from penguin except for the CKM factor including in
the diagram is small, then we can lead the allowed region of $R_t$ or $\phi_2$
by using the convention.
