COMET is an experiment to search for neutrinoless muon to electron conversion with a single-event of sensitivity of 3×10$^{-15}$ for Phase-I and 3 × 10$^{−17}$ for Phase-II which is a factor of 10,000 better than the current upper limit. In COMET Phase-I, the Cylindrical Drift Chamber (CDC) is the main part of the detection system. The purpose of CDC prototype IV was to finalise the parameters of CDC and to evaluate the detector performance of the CDC prototype. The beam test result without magnetic field was presented in last JPS meeting. In this meeting, I will present the analysis result of cosmic test of CDC prototype-4 with 1T magnetic field, which is conducted at cryogenic building.3 of KEK from 8th of May to 8th of June.