This study proposed and evaluated a method of measuring the thermal conductivity (TC) of drill cuttings from several igneous and pyroclastic rocks using the transient plane source principle, which allows quick and reliable measurements. The estimated bulk TCs of rocks were within an error of <10%, and suitable models were found. Measurements were applied to drill cuttings obtained along a well in the Hachimantai geothermal field, Japan, and TCs were obtained at ∼25 m intervals to a depth of 1700 m. Our analysis of the temperature profile using estimated TCs suggest the possible presence of fluid-flow zones in the well.