Provided is a radiation intensity measuring apparatus for each of small sealed radiation sources for cancer therapy capable of measuring multiple cartridges efficiently and rapidly. A radiation intensity measuring apparatus for radiation sources S in the state that the multiple radiation sources S are packed in a seed cartridge SC of a cartridge C, includes holding means 10 capable of holding the multiple cartridges C radiation intensity measuring means 30 for measuring intensity of the radiation emitted from the multiple radiation sources S and moving means 20 for moving the radiation intensity measuring means 30 toward or away from the holding means 10, and the radiation intensity measuring means 30 includes: a sensor 31 for measuring radiation intensity, and a shielding member 35 having a slit 35h provided for restricting radiation irradiated to the sensor 31 and the moving means 20 is configured to be able to relatively move the radiation intensity measuring means 30 along the direction in which the multiple radiation sources S are arranged in the measurement state.
