Dwarf spheroidal galaxies (dSphs) are promising targets of indirect detection experiments searching for dark matter (DM) at present universe. Toward robust prediction for the amount of signal flux originating in DM annihilation inside dSphs, a precise determination of DM distributions as well as $J$-factors of the dSphs is particularly important. In this work, we estimate those of Draco, Sculptor, and Ursa Minor dSphs by an improved statistical method in which both foreground stars and dSph member stars are simultaneously taken into account. We define the likelihood function of the method as the so-called conditional one to remove sampling bias of observed stellar data. This improved method enables us to estimate DM distributions and $J$-factors of the dSphs directly from observed stellar data contaminated by foreground stars without imposing stringent membership criteria on the measured quantities.
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