This paper investigates the stability of M2 demand in Japan using the statistical technique recently developed by Johansen (1988) and Johansen and Juselius (1989). Long-run equilibrium money demand function is identified and estimated along with the fourvariable vector error correction model (VECM). The results strongly suggests that the function shifted upwards - while leaving the income elasticity unchanged - in mid-1985, when the interest rates on large time deposits were deregulated.