  We calculate the effect of gravitational lensing on the parity-odd power
spectrum of the cosmic microwave background (CMB) polarization induced by
axionlike particles (ALPs). Several recent works have reported a tantalizing
hint of cosmic birefringence, a rotation of the linear polarization plane of
CMB, which ALPs can explain. In future CMB observations, we can measure cosmic
birefringence more precisely to get insight into ALPs. We find that the lensing
effect is necessary to fit the observed EB power spectrum induced by cosmic
birefringence in future CMB observations, including Simons Observatory and
CMB-S4. We also show that the estimated ALPs parameters are biased if we ignore
the lensing effect. Therefore, the lensing correction to the parity-odd power
spectra must be included in future high-resolution CMB experiments.
