A stator blade 13 has a blade tip 14, a blade trailing edge 15, a back 16 and a face 17. The blade tip 14 is an edge of the peripheral surface of the stator blade 13 near the turbine. The blade trailing edge 15 is an edge of the peripheral surface of the stator blade 13 near the impeller. The back 16 is a portion of the peripheral surface of the stator blade 13 extending between the blade tip 14 and the blade trailing edge 15 and opposed to the impeller 4, and has a streamline section. The face 17 is a portion of the peripheral surface of the stator blade 13 extending between the blade tip 14 and the blade trailing edge 15 and opposed to the turbine 5, and is formed of a streamline portion 17a and a plane portion 17b located near the blade tip 14. The shape of the stator blade 13 is such that a capacity coefficient (Cf) of a torque converter is lower when a speed ratio (e) is 0, and thereby improving fuel consumption during idling.