An inner image generating apparatus includes a first receiver configured to receive an inlet track information and a first passage time of a muon, a second receiver configured to receive an outlet track information and a second passage time of the muon, a displacement calculator configured to calculate a track displacement of a track of the muon based on the inlet and outlet track information, a mean energy calculator configured to calculate a mean energy of the muon based on a time-difference between the first passage and the second passage time, a data integration circuit configured to integrate multiplied data multiplying the track displacement and the mean energy on a projected plane, and an image generating circuit configured to generate an inner image of the structure by identifying a position of matter at the projected plane based on an integrated multiplied data.