PROBLEM TO BE SOLVED: To provide a beam emission protecting device of an accelerator capable of normally operating an electromagnet even when current of an electromagnet power supply decreases abnormally and surely stopping beam extraction during the abnormal operation of the power supply electromagnet.SOLUTION: According to an embodiment, a beam emission protecting device of an accelerator comprises: an electromagnet power supply 2 which supplies current to an electromagnet 1 of the accelerator a protective switch 3 connected to both ends on the output side of the electromagnet power supply 2 and operating as a switching element which can be electrically conducted with the electromagnet 1 when current of the electromagnet power supply 2 decreases abnormally an auxiliary power supply 6 connected in series to the electromagnet power supply 2 and capable of supplying current to the electromagnet 1 when the current of the electromagnet power supply 2 decreases abnormally a diode 5 connected between the protective switch 3 and the electromagnet 1 and operating as a rectifier element which rectifies the current so as to be supplied to the electromagnet 1 when the auxiliary power supply 6 is started and a beam stopping device 8 which obtains a stop signal from the electromagnet power supply 2 and stops the beam of the accelerator during current supply from the auxiliary power supply 6 when the current of the electromagnet power supply 2 decreases abnormally.
