A supercharger to pressurize an intake air for an engine, the supercharger comprising: a supercharger casing; a rotary unit provided in the supercharger and adapted to be rotatably accommodated within the supercharger casing; a planetary gear device through which a power is input to the rotary unit; and a bearing for supporting the rotary shaft in the supercharger casing, wherein the rotary unit comprises: a rotary shaft; an impeller fixed to a tip end portion of the rotary shaft; a rotating component rotatable together with the rotary shaft and being separate from the impeller; a fixing member to fix the impeller and the rotating component to the rotary shaft while pressing them in an axial direction of the rotary shaft; a non-rotating component which does not rotate together with the rotary shaft, the rotary unit being fixed to the supercharger casing through the non-rotating component, wherein the rotary unit comprises an adjustment portion for rotational balance adjustment, wherein the non-rotating component includes a bearing housing, which accommodates the bearing, and a stopper member to prevent an axial movement of the bearing housing, the bearing housing is supported in the supercharger casing for movement in a radial direction, the stopper member is fixed to the supercharger casing, and the rotary shaft has a base end portion connected with the planetary gear device, wherein the base end portion of the rotary shaft is formed with an externally threaded gear connected with the planetary gear device, and an end face of an inner ring of the bearing forming at least a portion of the rotating component is brought into contact with an end face of the externally threaded gear; a male threaded portion being formed on an outer peripheral surface of the tip end portion of the rotary shaft, and a nut member forming the fixing member being threadingly engaged with the male threaded portion; characterized in that the adjustment portion for rotational balance adjustment is formed in either the rotating component or the fixing member, wherein the male threaded portion is so set as to enable the nut member to be turned in a fastening direction when the rotary shaft is rotated; and the externally threaded gear is formed to represent a helical gear shape and is so configured that, when the rotary shaft is rotated, an axial force counter to the direction of a suction reactive force, which is generated due to rotation of the impeller, acts on the rotary shaft. a supercharger casing; a rotary unit provided in the supercharger and adapted to be rotatably accommodated within the supercharger casing; a planetary gear device through which a power is input to the rotary unit; and a bearing for supporting the rotary shaft in the supercharger casing, wherein the rotary unit comprises: a rotary shaft; an impeller fixed to a tip end portion of the rotary shaft; a rotating component rotatable together with the rotary shaft and being separate from the impeller; a fixing member to fix the impeller and the rotating component to the rotary shaft while pressing them in an axial direction of the rotary shaft; a non-rotating component which does not rotate together with the rotary shaft, the rotary unit being fixed to the supercharger casing through the non-rotating component, a rotary shaft; an impeller fixed to a tip end portion of the rotary shaft; a rotating component rotatable together with the rotary shaft and being separate from the impeller; a fixing member to fix the impeller and the rotating component to the rotary shaft while pressing them in an axial direction of the rotary shaft; a non-rotating component which does not rotate together with the rotary shaft, the rotary unit being fixed to the supercharger casing through the non-rotating component, wherein the rotary unit comprises an adjustment portion for rotational balance adjustment, wherein the non-rotating component includes a bearing housing, which accommodates the bearing, and a stopper member to prevent an axial movement of the bearing housing, the bearing housing is supported in the supercharger casing for movement in a radial direction, the stopper member is fixed to the supercharger casing, and the rotary shaft has a base end portion connected with the planetary gear device, wherein the base end portion of the rotary shaft is formed with an externally threaded gear connected with the planetary gear device, and an end face of an inner ring of the bearing forming at least a portion of the rotating component is brought into contact with an end face of the externally threaded gear; a male threaded portion being formed on an outer peripheral surface of the tip end portion of the rotary shaft, and a nut member forming the fixing member being threadingly engaged with the male threaded portion; characterized in that the adjustment portion for rotational balance adjustment is formed in either the rotating component or the fixing member, wherein the male threaded portion is so set as to enable the nut member to be turned in a fastening direction when the rotary shaft is rotated; and the externally threaded gear is formed to represent a helical gear shape and is so configured that, when the rotary shaft is rotated, an axial force counter to the direction of a suction reactive force, which is generated due to rotation of the impeller, acts on the rotary shaft.