Provided is a radiation intensity measuring apparatus for an encapsulated sealed radioactive source for brachytherapy capable of easily and accurately measuring radiation intensity of sources with a cartridge enclosed under sterile conditions.The radiation intensity measuring apparatus for sources S loaded in a cartridge C includes radiation intensity measuring means for measuring radiations emitted from the source S, holding means 30 for holding the cartridge C, and moving means for moving the holding means 30 to the radiation intensity measuring means. The moving means includes a guide portion for guiding the movement of the holding means 30 so that the holding means 30 moves along a direction perpendicular to an axial direction of a slit 15h, and a moving portion for moving the holding means 30 so that all the sources loaded in the cartridge C pass through a position of the slit 15h in housing space of a housing portion.
