A transparent optical material containing at least one selenium atom; a plastic lens made of the optical material; processes for producing these; and novel selenium compounds useful for producing the transparent optical material and plastic lens and represented by general formula (1), formula (2): (Z2) q - (SH) r, or formula (4): (Z?3) - (X2¿) s, wherein Y?1 and Z1¿ each represents C, S, etc.; X1 represents a polymerizable functional group such as SH, NCO, or acryloyl; Z¿2? represents alkylene containing at least one Se atom; q is an integer of 1 to 20; r is an integer of 3 to 6; Z?3¿ represents Se or alkylene containing at least one Se atom; X2 represents a functional group such as (meth)acrylol; and s is an integer of 2 to 6.