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Gas and dust properties in the Chamaeleon molecular cloud complex have beeninvestigated with emission lines from atomic hydrogen (HI) and 12CO molecule,dust optical depth at 353 GHz ($\tau_{353}$), and $J$-band infrared extinction($A_{J}$). We have found a scatter correlation between the HI integratedintensity ($W_{\rm HI}$) and $\tau_{353}$ in the Chamaeleon region. Thescattering has been examined in terms of possible large optical depth in HIemission ($\tau_{\rm HI}$) using a total column density ($N_{\rm H}$) modelbased on $\tau_{353}$. A nonlinear relation of $\tau_{353}$ with the $\sim$1.2power of $A_{J}$ has been found in opaque regions ($A_{J}$ $\gtrsim$ 0.3 mag),which may indicate dust evolution effect. If we apply this nonlinear relationto the $N_{\rm H}$ model (i.e., $N_{\rm H} \propto \tau_{353}^{1/1.2}$)allowing arbitrary $\tau_{\rm HI}$, the model curve reproduces well the $W_{\rmHI}$-$\tau_{353}$ scatter correlation, suggesting optically thick HI($\tau_{\rm HI} \sim$1.3) extended around the molecular clouds. Based on thecorrelations between the CO integrated intensity and the $N_{\rm H}$ model, wehave then derived the CO-to-H$_{2}$ conversion factor ($X_{\rm CO}$) on$\sim$1.5$^{\circ}$ scales (corresponding to $\sim$4 persec) and found spatialvariations of $X_{\rm CO}$ $\sim$(0.5-3)$\times$10$^{20}$ cm$^{-2}$ K$^{-1}$km$^{-1}$ s across the cloud complex, possibly depending on the radiation fieldinside or surrounding the molecular clouds. These gas properties found in theChamaeleon region are discussed through a comparison with other local molecularcloud complexes.

Gas and Dust Properties in the Chamaeleon Molecular Cloud Complex based on the Optically Thick HI