An image formation device including: a fixing unit that causes a sheet carrying a toner image to pass through a nipping part formed by bringing a rotary fixing member and a rotary pressure member into pressure contact with each other, so as to fix the toner image to the sheet; and an image formation device body having a fixing unit housing part that the fixing unit is to be removably housed in, an inserting and withdrawing direction of the fixing unit with respect to the fixing unit housing part agreeing with an axial direction of the rotary pressure member, a skeletal frame of the image formation device including columns (121, 122) making a pair that are so arranged as to be adjacent to the fixing unit housing part and spaced apart in the inserting and withdrawing direction of the fixing unit, and lateral beams (125, 127) making a pair that are orthogonally connected to the columns making a pair, respectively, as viewed in the inserting and withdrawing direction and support a bottom face of the fixing unit, the image formation device comprising: a driven gear integrally-rotatably coupled to a far end portion in the inserting and withdrawing direction of the rotary fixing member or the rotary pressure member of the fixing unit; a driving gear provided in a far end portion in the inserting and withdrawing direction of the fixing unit housing part and being to engage with the driven gear when the fixing unit is housed in the fixing unit housing part; and a drive source to rotatively drive the driving gear, wherein the driving gear and the driven gear are formed so that, during power transmission, a transmission force transmitted from a tooth flank of the driving gear to a tooth flank of the driven gear in a mutual engagement position has a component so directed as to horizontally press the fixing unit against the columns making a pair, and wherein the fixing unit as housed in the fixing unit housing part is pressed by the transmission force against the columns making a pair, and positioned in a direction orthogonal to the inserting and withdrawing direction. an inserting and withdrawing direction of the fixing unit with respect to the fixing unit housing part agreeing with an axial direction of the rotary pressure member, a skeletal frame of the image formation device including columns (121, 122) making a pair that are so arranged as to be adjacent to the fixing unit housing part and spaced apart in the inserting and withdrawing direction of the fixing unit, and lateral beams (125, 127) making a pair that are orthogonally connected to the columns making a pair, respectively, as viewed in the inserting and withdrawing direction and support a bottom face of the fixing unit, the image formation device comprising: a driven gear integrally-rotatably coupled to a far end portion in the inserting and withdrawing direction of the rotary fixing member or the rotary pressure member of the fixing unit; a driving gear provided in a far end portion in the inserting and withdrawing direction of the fixing unit housing part and being to engage with the driven gear when the fixing unit is housed in the fixing unit housing part; and a drive source to rotatively drive the driving gear, wherein the driving gear and the driven gear are formed so that, during power transmission, a transmission force transmitted from a tooth flank of the driving gear to a tooth flank of the driven gear in a mutual engagement position has a component so directed as to horizontally press the fixing unit against the columns making a pair, and wherein the fixing unit as housed in the fixing unit housing part is pressed by the transmission force against the columns making a pair, and positioned in a direction orthogonal to the inserting and withdrawing direction. a driven gear integrally-rotatably coupled to a far end portion in the inserting and withdrawing direction of the rotary fixing member or the rotary pressure member of the fixing unit; a driving gear provided in a far end portion in the inserting and withdrawing direction of the fixing unit housing part and being to engage with the driven gear when the fixing unit is housed in the fixing unit housing part; and a drive source to rotatively drive the driving gear, wherein the driving gear and the driven gear are formed so that, during power transmission, a transmission force transmitted from a tooth flank of the driving gear to a tooth flank of the driven gear in a mutual engagement position has a component so directed as to horizontally press the fixing unit against the columns making a pair, and wherein the fixing unit as housed in the fixing unit housing part is pressed by the transmission force against the columns making a pair, and positioned in a direction orthogonal to the inserting and withdrawing direction.