A one-way valve is arranged with an accumulator in a manner wherein the discharging of the accumulator is restricted. During upshifting, the stroking of a band brake servo in a release direction is induced before the charging stroke of the accumulator and the appropriate timing of the engagement of a high clutch (H/C) and the disengagement of a band brake (B/B) is induced. During downshifting, the pressure which is prevailing in the conduiting interconnecting the two friction elements is allowed to drop rapidly during the initial stage of the shift due to the provision of the one-way orifice (110) and allows the torque transmission capacity of the clutch to quickly reduce while inducing the stroking of the band brake servo in an engaging direction before the discharge stroke of the accumulator.