A beam data processing apparatus adapter to perform calculation processing of a state of a charged particle beam that has been accelerated by an accelerator and scanned by a scanning electromagnet (2, 3), the beam data processing apparatus comprising: - a plurality of channel data conversion units adapted to perform AD conversion processing in which each of the plurality of analogue signals output from a position monitor is converted into a digital signal; the position monitor being adapted to detects, with a plurality of detection channels, the passing position of the charged particle beam; - a position size processing unit adapted to calculate a beam position, which is the passing position of the charged particle beam in the position monitor, based on voltage information obtained through processing by the plurality of channel data conversion units; - an abnormality determination processing unit adapted to: determine whether or not the beam position is within a tolerance range, based on a desired position (Pd) of the charged particle beam and a position allowable value, and generate a position abnormality signal (sige1) when determining that the beam position is not within the tolerance range; - an integrated control unit adapted to control the plurality of channel data conversion units in such a way that while the charged particle beam is stopped at an irradiation spot, digital signal conversion processing is implemented two or more times, wherein each of the plurality of the channel data conversion units is connected to a respective channel of the position monitor, and a multiplexer adapted to switch the respective digital signals processed by the A/D converters at different timings so as to output the digital signals to the position size processing unit; characterised by: a demultiplexer adapted to distribute the respective analogue signals to the A/D converters at different timings, wherein further each of the plurality of the channel data conversion units has a plurality of A/D converters. - a plurality of channel data conversion units adapted to perform AD conversion processing in which each of the plurality of analogue signals output from a position monitor is converted into a digital signal; the position monitor being adapted to detects, with a plurality of detection channels, the passing position of the charged particle beam; - a position size processing unit adapted to calculate a beam position, which is the passing position of the charged particle beam in the position monitor, based on voltage information obtained through processing by the plurality of channel data conversion units; - an abnormality determination processing unit adapted to: determine whether or not the beam position is within a tolerance range, based on a desired position (Pd) of the charged particle beam and a position allowable value, and generate a position abnormality signal (sige1) when determining that the beam position is not within the tolerance range; determine whether or not the beam position is within a tolerance range, based on a desired position (Pd) of the charged particle beam and a position allowable value, and generate a position abnormality signal (sige1) when determining that the beam position is not within the tolerance range; - an integrated control unit adapted to control the plurality of channel data conversion units in such a way that while the charged particle beam is stopped at an irradiation spot, digital signal conversion processing is implemented two or more times, a demultiplexer adapted to distribute the respective analogue signals to the A/D converters at different timings, wherein further each of the plurality of the channel data conversion units has a plurality of A/D converters.