A vane motor comprising: a casing including a fluid inlet (135, 155) and a fluid outlet (133, 153), through which a pressurized fluid comes in or out; a rotor being installed in the casing, turning around a rotational shaft by the pressurized fluid and including a rotor body which has a substantially cylindrical shape and an axis coinciding with an axis of the rotational shaft and a plurality of vanes which is installed in grooves formed on an outer circumferential surface of the rotor body and has a portion protruding from the groove and (the portion) having a length varied in accordance with a rotational phase, wherein a - in respect of a rotation direction - rear edge portion of the opening of the groove formed on the rotor body to receive the vane is removed, to form an enlarged portion through which a rear surface of the vane is more exposed, wherein the casing is configured in such a way that both ends of an outer liner of a cylindrical shape are closed by disc-shaped finish plates (13, 15), at least one of the finish plates (13, 15) is configured in such a way that the rotational shaft pass throught and is exposed out of the finish plate (13, 15) to transmit the rotational force, characterized in that at least one of the finish plates (13, 15) is provided with the fluid inlet (135, 155) and the fluid outlet (133, 153), the enlarged portion is formed by partially removing at least one of the longitudinal ends of the groove from the opening of the rear edge portion of the groove, and a curved surface of the enlarged portion is formed as a concaved portion, when seen from the opening of the groove toward the inside of the groove and when seen from the end of the rotor body toward a center thereof in a longitudinal direction of the rotor body, and the fluid inlet (135, 155) is formed in such a way that it is aligned with the enlarged portion when the rotor turns and the enlarged portion is positioned to align with the fluid inlet (135, 155) of the finish plate (13, 15), thereby the portion of the groove joining the fluid inlet (135, 155) is enlarged by the enlarged portion. a casing including a fluid inlet (135, 155) and a fluid outlet (133, 153), through which a pressurized fluid comes in or out; a rotor being installed in the casing, turning around a rotational shaft by the pressurized fluid and including a rotor body which has a substantially cylindrical shape and an axis coinciding with an axis of the rotational shaft and a plurality of vanes which is installed in grooves formed on an outer circumferential surface of the rotor body and has a portion protruding from the groove and (the portion) having a length varied in accordance with a rotational phase, wherein a - in respect of a rotation direction - rear edge portion of the opening of the groove formed on the rotor body to receive the vane is removed, to form an enlarged portion through which a rear surface of the vane is more exposed, wherein the casing is configured in such a way that both ends of an outer liner of a cylindrical shape are closed by disc-shaped finish plates (13, 15), at least one of the finish plates (13, 15) is configured in such a way that the rotational shaft pass throught and is exposed out of the finish plate (13, 15) to transmit the rotational force, characterized in that at least one of the finish plates (13, 15) is provided with the fluid inlet (135, 155) and the fluid outlet (133, 153), the enlarged portion is formed by partially removing at least one of the longitudinal ends of the groove from the opening of the rear edge portion of the groove, and a curved surface of the enlarged portion is formed as a concaved portion, when seen from the opening of the groove toward the inside of the groove and when seen from the end of the rotor body toward a center thereof in a longitudinal direction of the rotor body, and the fluid inlet (135, 155) is formed in such a way that it is aligned with the enlarged portion when the rotor turns and the enlarged portion is positioned to align with the fluid inlet (135, 155) of the finish plate (13, 15), thereby the portion of the groove joining the fluid inlet (135, 155) is enlarged by the enlarged portion.