A fixing device for fixing a toner image onto a recording medium includes: an endless belt that is configured to be able to rotate; a pressure member that is in contact with an outer peripheral surface of the belt; and a sliding member that has a sliding surface in contact with an inner peripheral surface of the belt and is arranged to face the pressure member with the belt interposed between the sliding member and the pressure member, wherein a direction in which the belt rotating slides on the sliding surface is referred to as a direction of conveyance, a plurality of first grooves as well as a plurality of second grooves each allowing two of the plurality of first grooves adjacent to each other to communicate with each other are formed on the sliding surface, and the first grooves and the second grooves are formed in a non-grid pattern.