The object is to detect the irradiation position of a charged particle beam even when at an irradiation spot, a positional abnormality of the charged particle beam is caused. A beam data processing apparatus (11) has a plurality of channel data conversion units (21) that convert a plurality of analogue signals output from a position monitor (4) into digital signals, a position size processing unit (23) that calculates a beam position, based on voltage information items obtained through processing by the plurality of channel data conversion units (21), an abnormality determination processing unit (24) that determines the beam position and generates a position abnormality signal, and an integrated control unit (22) that controls the plurality of channel data conversion units (21) in such a way that while a beam is stopped at an irradiation spot, digital signal conversion processing is implemented two or more times the channel data conversion unit (21) has a plurality of A/D converters (33), a demultiplexer (32) that distributes analogue signals, and a multiplexer (34) that switches respective digital signals processed by the A/D converters so as to output them to the position size processing unit (23).
