  We present cosmological constraints on the scalar-tensor theory of gravity by
analyzing the angular power spectrum data of the cosmic microwave background
obtained from the Planck 2015 results together with the baryon acoustic
oscillations (BAO) data. We find that the inclusion of the BAO data improves
the constraints on the time variation of the effective gravitational constant
by more than $10\%$, that is, the time variation of the effective gravitational
constant between the recombination and the present epochs is constrained as
$G_{\rm rec}/G_0-1 <1.9\times 10^{-3}\ (95.45\%\ {\rm C.L.})$ and $G_{\rm
rec}/G_0-1 <5.5\times 10^{-3}\ (99.99 \%\ {\rm C.L.})$. We also discuss the
dependence of the constraints on the choice of the prior.
