A thinning detection system comprising: a current applying apparatus configured to apply an AC current to electrodes installed on metal equipment which is a thinning detection object on which thinning detection is performed; a magnetic-field measuring apparatus including an array of magnetic sensors configured to measure a magnetic field distribution of a surface side of the metal equipment; and a measurement managing apparatus configured to estimate a thinning distribution of the metal equipment on the basis of a magnetic field distribution difference which is a difference between a reference magnetic-field distribution which is obtained in a case where thinning has not occurred in the metal equipment and a measurement magnetic-field distribution which is an actual measurement result, wherein the measurement managing apparatus is configured to calculate a virtual current distribution of the metal equipment from the magnetic field distribution difference, and to estimate the thinning distribution of the metal equipment on the basis of a virtual eddy current represented by the virtual current distribution, wherein the virtual eddy current is a difference between a current distribution which is obtained in the case where thinning has not occurred in the metal equipment and a current distribution which is obtained in a case where thinning has occurred in the metal equipment, and characterized in that: the measurement managing apparatus is configured to: estimate a thinning shape on the basis of a spiral direction of the virtual eddy current; and estimate a thinning depth on the basis of a density of the virtual eddy current. a current applying apparatus configured to apply an AC current to electrodes installed on metal equipment which is a thinning detection object on which thinning detection is performed; a magnetic-field measuring apparatus including an array of magnetic sensors configured to measure a magnetic field distribution of a surface side of the metal equipment; and a measurement managing apparatus configured to estimate a thinning distribution of the metal equipment on the basis of a magnetic field distribution difference which is a difference between a reference magnetic-field distribution which is obtained in a case where thinning has not occurred in the metal equipment and a measurement magnetic-field distribution which is an actual measurement result, wherein the measurement managing apparatus is configured to calculate a virtual current distribution of the metal equipment from the magnetic field distribution difference, and to estimate the thinning distribution of the metal equipment on the basis of a virtual eddy current represented by the virtual current distribution, wherein the virtual eddy current is a difference between a current distribution which is obtained in the case where thinning has not occurred in the metal equipment and a current distribution which is obtained in a case where thinning has occurred in the metal equipment, and characterized in that: the measurement managing apparatus is configured to: estimate a thinning shape on the basis of a spiral direction of the virtual eddy current; and estimate a thinning depth on the basis of a density of the virtual eddy current. estimate a thinning shape on the basis of a spiral direction of the virtual eddy current; and estimate a thinning depth on the basis of a density of the virtual eddy current.