A charged particle detecting device according to the present invention includes an electron detecting portion, a signal processing portion, a selection portion, an accumulation portion configured to accumulate information on a muon, and a computation portion. The electron detecting portion detects an ionized electron generated along a trajectory of a charged particle flying within a scatterer. The signal processing portion processes a signal detected by the electron detecting portion, to thereby acquire information on the charged particle. The selection portion selects information on a muon from the information on the charged particle detected by the signal processing portion. The computation portion acquires a coefficient for sensitivity in detection of the information on the charged particle based on the accumulated information on the muon.