  It is shown in the framework of the operator product expansion and the
renormalization group method that the twist-3 part of flavour nonsinglet spin
structure function g_2(x,Q^2) obeys a simple Dokshitzer-Gribov-
Lipatov-Altarelli-Parisi (DGLAP) equation in the large N_C limit even in the
case of massive quarks (N_C is the number of colours). There are four different
types of twist-3 operators which contribute to g_2, including
quark-mass-dependent operators and the ones proportional to the equation of
motion. They are not all independent but are constrained by one relation. A new
choice of the independent operator bases leads to a simple form of the
evolution equation for g_2 at large N_C.
