PURPOSE: To make high speed sensing of gamma rays at any desired angle by furnishing a rotary ring consisting of magnetic substance rotatably in a ring-shaped vacuum tube installed in such a way as surrounding a patient.

CONSTITUTION: A patient 100 is irradiated with radioactive isotope, and thereby gamma rays 50 are emitted from the patient 100. A rotor 10 is rotated at a certain speed to enable sensing while the patient 100 lies in any position. The gamma rays 50 emitted from the patient 100 on a bed in the desired position of rotational angle run against a scintillator 1, and light 51 is generated by the photo-electric effect. A dynode 2 converts this light 51 into electrons 52, which are gathered at an anode 3 and led to the outside via a lead. Both the dynode 2 and anode 3 are made in ring form and secured to the inner surface of a doughnut-shaped vacuum tube 15. Even though the scintillator 1 is in any position of rotational angle, therefore, the dosage of gamma rays received in this position can be sensed by the anode 3. As a result, the amount gamma rays around the patient 100 can be taken out at a high speed together with the angle signal.