There is provided a fixing device for thermally fixing a developing agent image to a sheet. The fixing device includes a tubular flexible member, a heater, a nip member and a backup member. The tubular flexible member has an inner peripheral surface defining an internal space. The heater is disposed within the internal space and is configured to generate a radiant heat. The nip member is disposed within the internal space and is configured to receive the radiant heat from the heater, the inner peripheral surface being in sliding contact with the nip member, and the nip member being electrically conductive and the tubular flexible member being grounded via the nip member. The backup member is configured to provide a nip region in cooperation with the nip member for nipping the tubular flexible member between the backup member and the nip member.