In dental clinic, some lasers have already realized the optical drilling of dental hard tissue. However, conventional lasers lack the ability to discriminate and excavate carious tissue only, and still depend on the dentist's ability. The objective of this study is to develop a selective excavation of carious dentin by using the laser ablation with 6 μm wavelength range. Bovine dentin demineralized with lactic acid solution was used as a carious dentin model. A mid-infrared tunable pulsed laser was obtained by difference-frequency generation technique. The wavelength was tuned around the absorption bands called amide 1 and amide 2. In the wavelength range from 5.75 to 6.60 μm, the difference of ablation depth between demineralized and normal dentin was observed. The wavelength at 6.02 μm and the average power density of 15 W/cm(2), demineralized dentin was removed selectively with less-invasive effect on normal dentin. The wavelength at 6.42 μm required the increase of average power density, but also showed the possibility of selective ablation. In the near future, development of compact laser device will open the minimal invasive laser treatment to the dental clinic.