A variable nozzle turbocharger which varies exhaust gas blown to a turbine wheel through a nozzle path, the variable nozzle turbocharger comprising: a plurality of nozzle vanes provided in the nozzle path; a plurality of arms each having a pivoted end and a free end, the pivoted end being integrally coupled with the nozzle vane by means of a pivot; a unison ring provided with a plurality of grooves each of which is engaged with the respective free end of the arm, wherein when the unison ring rotates in both an opening direction to increase a cross sectional area of the nozzle path and a closing direction to decrease the cross sectional area of the nozzle path, the free end engaged with the groove of the unison ring rotates with the unison ring, and the arm and the nozzle vane rotate integrally with the free end about an axis of the pivot in the opening direction and the closing direction to vary the cross sectional area of the nozzle path, wherein the free end of the arm has a first contact surface on a side on which the arm rotates in the closing direction and a second contact surface on a side on which the arm rotates in the opening direction, the first contact surface and the second contact surface being each in contact with a respective one of paired walls forming the groove of the unison ring, both of the first contact surface and the second contact surface of the arm each forming a curved surface convexed toward a respective wall surface of the groove of the unison ring, the first contact surface having a first proximal edge which is a peripheral edge closer to the pivot and a first distal edge which is a peripheral edge farther away from the pivot, the second contact surface having a second proximal edge which is a peripheral edge closer to the pivot and a second distal edge which is a peripheral edge farther away from the pivot, characterized by one of the first contact surface and the second contact surface having a curvature continuously made smaller from the proximal edge toward the distal edge with a radius of curvature gradually made larger from the proximal edge toward the distal edge and the other of the first contact surface and the second contact surface having a curvature continuously made larger from the proximal edge toward the distal edge with a radius of curvature gradually made larger from the distal edge toward the proximal edge, and in that the paired walls of the groove are formed parallel to each other. a plurality of nozzle vanes provided in the nozzle path; a plurality of arms each having a pivoted end and a free end, the pivoted end being integrally coupled with the nozzle vane by means of a pivot; a unison ring provided with a plurality of grooves each of which is engaged with the respective free end of the arm, wherein when the unison ring rotates in both an opening direction to increase a cross sectional area of the nozzle path and a closing direction to decrease the cross sectional area of the nozzle path, the free end engaged with the groove of the unison ring rotates with the unison ring, and the arm and the nozzle vane rotate integrally with the free end about an axis of the pivot in the opening direction and the closing direction to vary the cross sectional area of the nozzle path, wherein the free end of the arm has a first contact surface on a side on which the arm rotates in the closing direction and a second contact surface on a side on which the arm rotates in the opening direction, the first contact surface and the second contact surface being each in contact with a respective one of paired walls forming the groove of the unison ring, both of the first contact surface and the second contact surface of the arm each forming a curved surface convexed toward a respective wall surface of the groove of the unison ring, the first contact surface having a first proximal edge which is a peripheral edge closer to the pivot and a first distal edge which is a peripheral edge farther away from the pivot, the second contact surface having a second proximal edge which is a peripheral edge closer to the pivot and a second distal edge which is a peripheral edge farther away from the pivot, characterized by one of the first contact surface and the second contact surface having a curvature continuously made smaller from the proximal edge toward the distal edge with a radius of curvature gradually made larger from the proximal edge toward the distal edge and the other of the first contact surface and the second contact surface having a curvature continuously made larger from the proximal edge toward the distal edge with a radius of curvature gradually made larger from the distal edge toward the proximal edge, and in that the paired walls of the groove are formed parallel to each other.