An excitation inrush current suppression device configured for suppressing excitation inrush currents flowing through a breaker for opening and closing connection between a three-phase AC power system including a power supply and an effectively grounded transformer that converts a three-phase AC voltage to single-phase AC voltages of two sections, the device characterized by comprising: a transformer-side single-phase AC voltage measurement unit configured to measure single-phase AC voltages on a transformer-side of the breaker; a residual magnetic flux calculation unit configured to perform calculation, based on the single-phase AC voltages measured by the transformer-side single-phase AC voltage measurement unit, to calculate residual magnetic fluxes of three phases of the transformer after the transformer is shut off by the breaker; a power supply-side three-phase AC voltage measurement unit configured to measure a three-phase AC voltage on a power supply-side of the breaker; a prospective magnetic flux calculation unit configured to perform calculation, based on the three-phase AC voltage measured by the power supply-side three-phase AC voltage measurement unit, to calculate prospective magnetic fluxes of the three phases of the transformer; a phase position determination unit configured to determine a phase position at which polarities of the prospective magnetic fluxes of the three phases calculated by the prospective magnetic flux calculation unit respectively agree with polarities of the residual magnetic fluxes of the three phases calculated by the residual magnetic flux calculation unit in all of the three phases respectively; and a closing unit configured to set the breaker closed, for the three phases all together, at the phase position determined by the phase position determination unit. a transformer-side single-phase AC voltage measurement unit configured to measure single-phase AC voltages on a transformer-side of the breaker; a residual magnetic flux calculation unit configured to perform calculation, based on the single-phase AC voltages measured by the transformer-side single-phase AC voltage measurement unit, to calculate residual magnetic fluxes of three phases of the transformer after the transformer is shut off by the breaker; a power supply-side three-phase AC voltage measurement unit configured to measure a three-phase AC voltage on a power supply-side of the breaker; a prospective magnetic flux calculation unit configured to perform calculation, based on the three-phase AC voltage measured by the power supply-side three-phase AC voltage measurement unit, to calculate prospective magnetic fluxes of the three phases of the transformer; a phase position determination unit configured to determine a phase position at which polarities of the prospective magnetic fluxes of the three phases calculated by the prospective magnetic flux calculation unit respectively agree with polarities of the residual magnetic fluxes of the three phases calculated by the residual magnetic flux calculation unit in all of the three phases respectively; and a closing unit configured to set the breaker closed, for the three phases all together, at the phase position determined by the phase position determination unit.