  We study systematic uncertainties in the lattice QCD computation of hadronic
vacuum polarization (HVP) contribution to the muon $g-2$. We investigate three
systematic effects; finite volume (FV) effect, cutoff effect, and integration
scheme dependence. We evaluate the FV effect at the physical pion mass on two
different volumes of (5.4 fm$)^4$ and (10.8 fm$)^4$ using the PACS10
configurations at the same cutoff scale. For the cutoff effect, we compare two
types of lattice vector operators, which are local and conserved
(point-splitting) currents, by varying the cutoff scale on a larger than (10
fm$)^4$ lattice at the physical point. For the integration scheme dependence,
we compare the results between the coordinate- and momentum-space integration
schemes at the physical point on a (10.8 fm$)^4$ lattice. Our result for the
HVP contribution to the muon $g-2$ is given by $a_\mu^{\rm hvp} =
737(9)(^{+13}_{-18})\times 10^{-10}$ in the continuum limit, where the first
error is statistical and the second one is systematic.
