Comparison of 1 Myr isochrones for the cases X_D = 35 (red lines) and 20 ppm (blue) ranging ξ from 0 (dotted) to 0.5 (solid), respectively. The initial radius is 1.5 R_⊙. The points for observation and isochrones are the same as in Fig. 8. The isochrone with (X_D,ξ) = (35 ppm,0) is almost the same as that with (20 ppm, 0.1), implying that the different deuterium content has a large impact on the PMS evolution. The thin solid line is a 1 Myr non-accreting isochrone (Baraffe et al. 1998).