A fixing device includes a heat generating member, an endless belt, and a heat conductive member that contacts the heat generating member in a first region. A positioning portion is provided at an end portion of the heat conductive member, so as to extend in a direction in which the positioning portion is spaced apart from the heat generating member. A supporting member is provided with a first opening at a position corresponding to a second region of the heat generating member, and supports the heat generating member via the heat conductive member. An electrical power shut-off member, located in the first opening of the supporting member, shuts off electrical power supplied to the heat generating member. The positioning portion is inserted into the first opening of the supporting member to prevent movement of the heat conductive member.