The exhaust gas purifying device of an internal combustion engine includes: an electrically heated catalyst which is provided on an exhaust passage of the internal combustion engine, which purifies the exhaust gas drawn to the exhaust passage, and is warmed by electrification; and an electrification characteristic setting unit which set an electrification characteristic indicating a characteristic of an electrification resistance value in the electrically heated catalyst, in accordance with an electrification condition at a time of starting the electrification of the electrically heated catalyst. Thus, various determinations and controls relating to the electrically heated catalyst and using the electrification characteristic can be accurately performed.