A fixing device according to an embodiment includes a first rotating body, a pressing unit, an urging member, a base body section, a screw shaft section, and a rotation regulating section. The pressing unit includes a belt, a second rotating body, and a supporting frame. The supporting frame supports the second rotating body. The urging member urges the pressing unit in a direction in which the second rotating body approaches the first rotating body. The base body section is rotatable around an axis. The shape of a cross section of the base body section orthogonal to an axial direction is a noncircular shape. The screw shaft section projects from the base body section and regulates a movement of the pressing unit in a direction in which the pressing unit approaches the first rotating body. The rotation regulating section comes into contact with the outer surface of the base body section to regulate the rotation of the base body section.