An image forming apparatus includes a charging roller, a temperature sensor, a humidity sensor, a sampling part, a life consumption degree calculating part and a warning processing part. The sampling part executes temperature/humidity inputting process inputting temperature of the temperature sensor and humidity of the humidity sensor. The life consumption degree calculating part calculates a life consumption degree of the charging roller from a last time to a present time in the temperature/humidity inputting process by applying respective representative values of last and present inputted temperature and humidity into a model formula. The warning processing part outputs a warning when an addition value of the life consumption degrees exceeds a predetermined threshold value. The life consumption degree calculating part uses the model formula deriving larger life consumption degree in a case where the representative value of the temperature and the representative value of the humidity are respectively larger.