Abstract: A method for polarizing nuclear spins includes a process to apply a static magnetic field to NV centers, a process to irradiate the NV centers with a first microwave having a first microwave wavelength to transition energy levels ms of electron spins of the NV centers of which energy levels ml of nuclear spins are one of ml=1 or ?1 from ms=0 to ms=?1, and a process to irradiate the NV centers with a second microwave having a second microwave wavelength different from the first microwave wavelength to transition the energy levels ms of electron spins of the NV centers of which the energy levels ml of the nuclear spins are the other of ml=1 or ?1 from ms=0 to ms=?1 when a microwave irradiation waiting period determined depending on the period of state mixing of polarization of the nuclear spins has elapsed since the irradiation with the first microwave.