A device for use in a vertical washing machine, the vertical washing machine having a cylindrical washing tank with a bottom and is formed with an access port for laundry at an upper end and is provided with a bottom wall at a lower end; the device comprises: a main body, having a back face which is opposite to an inner circumferential face of the washing tank and a surface which is located on an opposite side of the back face and faces a central axis side of the washing tank; wherein the main body is mountable on the inner circumferential face of the washing tank in a posture along the up-down direction; an intake port, which is provided at a lower end portion of the main body for introducing water in the washing tank from a bottom wall side; a waterway, which is provided in the main body for guiding the water introduced by the intake port upwardly; and an exhaust port, which is provided on a surface of an upper end portion of the main body for exhausting the water guided by the waterway and splashing the water onto laundry in the washing tank, wherein the exhaust port is relatively long in a circumferential direction of the inner circumferential face of the washing tank, a top-to-bottom width of the exhaust port in the middle of the circumferential direction is narrower than that at both ends in the circumferential direction, and grooves on the surface of the main body are adjacently arranged on two outer sides of the exhaust port in the circumferential direction; characterized in that each groove is formed to be recessed toward the back face of the body and extends in the up-down direction beyond the top-to-bottom width of the exhaust port at both ends in the circumferential direction, the surface of the upper end portion of the body is pressed toward an inner side in the circumferential direction, and the exhaust port is bordered into a substantially arc shape bulged toward the central axis side of the washing tank. a main body, having a back face which is opposite to an inner circumferential face of the washing tank and a surface which is located on an opposite side of the back face and faces a central axis side of the washing tank; wherein the main body is mountable on the inner circumferential face of the washing tank in a posture along the up-down direction; an intake port, which is provided at a lower end portion of the main body for introducing water in the washing tank from a bottom wall side; a waterway, which is provided in the main body for guiding the water introduced by the intake port upwardly; and an exhaust port, which is provided on a surface of an upper end portion of the main body for exhausting the water guided by the waterway and splashing the water onto laundry in the washing tank, wherein the exhaust port is relatively long in a circumferential direction of the inner circumferential face of the washing tank, a top-to-bottom width of the exhaust port in the middle of the circumferential direction is narrower than that at both ends in the circumferential direction, and grooves on the surface of the main body are adjacently arranged on two outer sides of the exhaust port in the circumferential direction; characterized in that each groove is formed to be recessed toward the back face of the body and extends in the up-down direction beyond the top-to-bottom width of the exhaust port at both ends in the circumferential direction, the surface of the upper end portion of the body is pressed toward an inner side in the circumferential direction, and the exhaust port is bordered into a substantially arc shape bulged toward the central axis side of the washing tank.