  To understand the origin of nuclear ($\lesssim$ 100 pc) millimeter-wave
(mm-wave) continuum emission in active galactic nuclei (AGNs), we
systematically analyzed sub-arcsec resolution Band-6 (211-275 GHz) ALMA data of
98 nearby AGNs ($z <$ 0.05) from the 70-month Swift/BAT catalog. The sample,
almost unbiased for obscured systems, provides the largest number of AGNs to
date with high mm-wave spatial resolution sampling ($\sim$ 1-200 pc), and spans
broad ranges of 14-150 keV luminosity {$40 < \log[L_{\rm 14-150}/({\rm
erg\,s^{-1}})] < 45$}, black hole mass [$5 < \log(M_{\rm BH}/M_\odot) < 10$],
and Eddington ratio ($-4 < \log \lambda_{\rm Edd} < 2$). We find a significant
correlation between 1.3 mm (230 GHz) and 14-150 keV luminosities. Its scatter
is $\approx$ 0.36 dex, and the mm-wave emission may serve as a good proxy of
the AGN luminosity, free of dust extinction up to $N_{\rm H} \sim 10^{26}$
cm$^{-2}$. While the mm-wave emission could be self-absorbed synchrotron
radiation around the X-ray corona according to past works, we also discuss
different possible origins of the mm-wave emission; AGN-related dust emission,
outflow-driven shocks, and a small-scale ($<$ 200 pc) jet. The dust emission is
unlikely to be dominant, as the mm-wave slope is generally flatter than
expected. Also, due to no increase in the mm-wave luminosity with the Eddington
ratio, a radiation-driven outflow model is possibly not the common mechanism.
Furthermore, we find independence of the mm-wave luminosity on indicators of
the inclination angle from the polar axis of the nuclear structure, which is
inconsistent with a jet model whose luminosity depends only on the angle.
