A fixing device includes a fixing member, a pressing member, a temperature detector, and a heater. The pressing member contacts an outer circumferential surface of the fixing member to form a fixing nip between the fixing member and the pressing member through which a recording medium bearing a toner image passes. The heater heats the fixing member to a predetermined temperature based on a detection result provided by the temperature detector. A circumferential distance A between the temperature detector and the heater along a circumference of the fixing member is defined by the following formula: A≧v×(T1+T2) where v is a circumferential velocity of the fixing member rotating in a predetermined direction of rotation, T1 is a response time of the temperature detector, and T2 is a response time of the heater.