A method and apparatus for detecting radioactivity of a whole body is disclosed. The apparatus for detecting radioactivity of a whole body is divided into upper and lower parts, the upper and lower parts are divided into front, rear, left and right portions, respectively, a radioactivity detection unit is installed at each of the front, rear, left and right portions, radioactivity values detected by each of the radioactivity detection units are compared and analyzed such that radioactivity values detected by the radioactivity detection units positioned at upper front and rear parts are compared, radioactivity values detected by the radioactivity detection units positioned at upper left and right parts are compared, and also radioactivity values detected by the lower radioactivity detection units are compared in the same manner, thus determining whether or not the internal parts or external parts of the body of a detection target have been contaminated by radioactivity.