An adjustment device of a rotary machine including a movable base formed rotatable around an axis, vibration sensors formed so that the sensors can measure amplitudes of longitudinal vibration and transverse vibration of the rotary machine, an adjustment weight to be arranged on the movable base, and a PC including a control section for calculating a position and weight of the adjustment weight, a storage section, and an amplifier are provided, an approximate expression is obtained by the PC from an amplitude measured by the vibration sensor, and a predetermined function, an optimum change amount x and position .theta. of the adjustment weight are calculated from the approximate expression, whereby the adjustment weight is arranged.