PROBLEM TO BE SOLVED: To provide a position detection apparatus capable of preventing reading of a wrong BCD signal in the midst of an A/D conversion process of the BCD signal output from an A/D converter that is used in the position detection device of an in-reactor neutron flux detector.SOLUTION: A timing generation part 6a of an FPGA 6 disposed for inputting a BCD signal 10 of an A/D converter 2 outputs an output timing signal 12a of a hold signal 12 to an A/D conversion part 6b; the hold function of the A/D converter 2 holds the BCD signal 10 for a first predetermined time Tto hold update of data at the final stage; when an input circuit part 6c disposed for inputting a read timing signal 16 reads the BCD signal held within a second predetermined time Tthat is within the range of the first predetermined time Tand also inputs a hold-canceling signal 13, update of data is restarted so that the FPGA 6 performs transmission to a card 4 and an external CPU 8 via a serial I/O 7.
