A technique for the writing of crystal line in glass has been developed, in which a continuous-wave Nd:YAG laser (wavelength: λ=1064 nm) is irradiated to the glasses containing transition metal (TM) ions such as Fe2+, Ni2+, and V4+. Laser energies are absorbed through d-d transitions of TM ions and dissipated to the lattice surrounding TM ions by nonradiative relaxation process, giving the increase in temperature in the laser irradiated region and inducing crystallization. This technique has been demonstrated for the writing of crystal lines consisting of nonlinear optical fresnoite-type Ba2 Ti Ge2 O8 and Ba2 Ti Si2 O8 crystals in NiO-, Fe2 O3 -, and V2 O5 -doped (0.3-1 mol %) BaO-Ti O2 -Ge O2 and BaO-Ti O2 -Si O2 glasses. It is confirmed that crystals in the crystal lines are highly oriented along the laser scanning direction. The technique developed in this study is proposed to be called "transition metal atom heat processing."