A fixing device to be used with an image forming device comprising: a fixing member; a pressure member which is brought into press contact with the fixing member and is configured to form a nip portion at which the pressure member interposes a paper carrying an unfixed toner image between the fixing member and the pressure member, to melt the unfixed toner image, and to fix the molten toner image to the paper; and a nip pressure adjustment mechanism that is configured to adjust nip pressure of the nip portion, wherein the nip pressure adjustment mechanism comprises: an arm member that supports the pressure member at one end side such that the pressure member freely rotates; a compression spring that presses the other end side of the arm member to press the pressure member to the fixing member; a lever provided at the other end side of the arm member in parallel to the arm member and pressed at spring pressure of the compression spring together with the arm member; a roller supported by the lever so as to freely rotate; an eccentric cam provided at the lateral side of the lever so as to be rotatable in parallel to the lever, and abutting the roller; and a driving gear train (40, 41, 42, 43, 44, and 45) that is configured to transmit driving force to the eccentric cam to rotate the eccentric cam, wherein the eccentric cam has a maximum radius part and a minimum radius part provided at a position separated from the maximum radius part and configured with a bottom surface of a bottomed concave portion opened outward in a radial direction, and characterized in that the pressure member is configured to be brought into press contact with the fixing member at the spring pressure of the compression spring via the lever and the arm member, when the roller faces the concave portion, and to move in a direction separating from the fixing member via the lever and the arm member against the spring pressure of the compression spring, when the roller faces the maximum radius part. a fixing member; a pressure member which is brought into press contact with the fixing member and is configured to form a nip portion at which the pressure member interposes a paper carrying an unfixed toner image between the fixing member and the pressure member, to melt the unfixed toner image, and to fix the molten toner image to the paper; and a nip pressure adjustment mechanism that is configured to adjust nip pressure of the nip portion, wherein the nip pressure adjustment mechanism comprises: an arm member that supports the pressure member at one end side such that the pressure member freely rotates; a compression spring that presses the other end side of the arm member to press the pressure member to the fixing member; a lever provided at the other end side of the arm member in parallel to the arm member and pressed at spring pressure of the compression spring together with the arm member; a roller supported by the lever so as to freely rotate; an eccentric cam provided at the lateral side of the lever so as to be rotatable in parallel to the lever, and abutting the roller; and a driving gear train (40, 41, 42, 43, 44, and 45) that is configured to transmit driving force to the eccentric cam to rotate the eccentric cam, wherein the eccentric cam has a maximum radius part and a minimum radius part provided at a position separated from the maximum radius part and configured with a bottom surface of a bottomed concave portion opened outward in a radial direction, and characterized in that the pressure member is configured to be brought into press contact with the fixing member at the spring pressure of the compression spring via the lever and the arm member, when the roller faces the concave portion, and to move in a direction separating from the fixing member via the lever and the arm member against the spring pressure of the compression spring, when the roller faces the maximum radius part. an arm member that supports the pressure member at one end side such that the pressure member freely rotates; a compression spring that presses the other end side of the arm member to press the pressure member to the fixing member; a lever provided at the other end side of the arm member in parallel to the arm member and pressed at spring pressure of the compression spring together with the arm member; a roller supported by the lever so as to freely rotate; an eccentric cam provided at the lateral side of the lever so as to be rotatable in parallel to the lever, and abutting the roller; and a driving gear train (40, 41, 42, 43, 44, and 45) that is configured to transmit driving force to the eccentric cam to rotate the eccentric cam, wherein the eccentric cam has a maximum radius part and a minimum radius part provided at a position separated from the maximum radius part and configured with a bottom surface of a bottomed concave portion opened outward in a radial direction, and characterized in that the pressure member is configured to be brought into press contact with the fixing member at the spring pressure of the compression spring via the lever and the arm member, when the roller faces the concave portion, and to move in a direction separating from the fixing member via the lever and the arm member against the spring pressure of the compression spring, when the roller faces the maximum radius part.