A decommissioning method of biological shielding concrete of a nuclear power plant according to an exemplary embodiment includes: decommissioning a neutron detector positioning device installed to biological shielding concrete surrounding a nuclear reactor to form a plurality of penetrated parts in the biological shielding concrete; inserting a part of a cutting device into the plurality of penetrated parts; and decomposing the biological shielding concrete into a plurality of sub-concrete parts by using the cutting device.