A muon tracker includes a drift tube detector having a plurality of drift tube arrays, a detection time-difference calculation circuit configured to calculate a detected time-difference between a plurality of time data detected at least two of the drift tubes, a time-difference information database that stores a relationship between a plurality of predetermined tracks of the muon passing the drift tube detector and a predetermined time-difference of possible detected time data to be detected at least two of the drift tubes where each of the plurality of predetermined tracks passes, a time-difference referring circuit configured to refer the detected time-difference calculated at the detection time-difference calculation circuit with the predetermined time-difference stored in the time-difference information database, and a muon track determining circuit configured to determine a muon track as the predetermined track of the muon corresponding to the predetermined time-difference that matches the best with the detected time-difference.