It is an object of the present invention to make it possible to stably and correctly measure a changing amount of a beam position when a beam displacement is measured prior to a recording operation performed by an electron beam recording apparatus. A BIST controller is used to address the memory and provide reference data that is compared to the memory output. A plunger is movable in the barrel, and has an engaging head defining a rearwardly facing shoulder wall which is retained by the catch when the engaging head is extended into the cavity by a pushing force applied to the plunger.