An electric stapler, comprising: a clamp part that is configured to include a first wall portion and a second wall portion facing each other with a predetermined gap therebetween, in which the first wall portion is movable in directions of approaching and separating from the second wall portion, and that grips a paper bundle inserted between the first wall portion and the second wall portion by moving the first wall portion in the direction of approaching the second wall portion; a penetration part that causes a staple to penetrate the paper bundle gripped by the clamp part; a clinch part that bends the staple penetrating the paper bundle to bind the paper bundle; a gripping release detection unit that detects that the paper bundle is released from gripping after the first wall portion moves in the direction of separating from the second wall portion from a state where the paper bundle is gripped by the clamp part; an output unit that, after it is detected that the paper bundle is released from gripping of the clamp part, outputs a gripping release signal indicating that the paper bundle is released from gripping of the clamp part to an outside; and a motor that moves the first wall portion, wherein the first wall portion moves in accordance with a rotation amount of the motor, and wherein the gripping release detection unit detects, based on a rotation amount of the motor, that the paper bundle is released from gripping characterized in that the electric stapler further comprises: a load fluctuation detection unit that detects load fluctuation of the motor at a time when the clamp part grips the paper bundle with the first wall portion and the second wall portion; and a thickness estimation unit that estimates a thickness of the paper bundle based on the load fluctuation, wherein the gripping release detection unit detects, based on the estimated thickness of the paper bundle, that the paper bundle is released from gripping of the clamp part. a clamp part that is configured to include a first wall portion and a second wall portion facing each other with a predetermined gap therebetween, in which the first wall portion is movable in directions of approaching and separating from the second wall portion, and that grips a paper bundle inserted between the first wall portion and the second wall portion by moving the first wall portion in the direction of approaching the second wall portion; a penetration part that causes a staple to penetrate the paper bundle gripped by the clamp part; a clinch part that bends the staple penetrating the paper bundle to bind the paper bundle; a gripping release detection unit that detects that the paper bundle is released from gripping after the first wall portion moves in the direction of separating from the second wall portion from a state where the paper bundle is gripped by the clamp part; an output unit that, after it is detected that the paper bundle is released from gripping of the clamp part, outputs a gripping release signal indicating that the paper bundle is released from gripping of the clamp part to an outside; and a motor that moves the first wall portion, wherein the first wall portion moves in accordance with a rotation amount of the motor, and wherein the gripping release detection unit detects, based on a rotation amount of the motor, that the paper bundle is released from gripping characterized in that the electric stapler further comprises: a load fluctuation detection unit that detects load fluctuation of the motor at a time when the clamp part grips the paper bundle with the first wall portion and the second wall portion; and a thickness estimation unit that estimates a thickness of the paper bundle based on the load fluctuation, wherein the gripping release detection unit detects, based on the estimated thickness of the paper bundle, that the paper bundle is released from gripping of the clamp part. a load fluctuation detection unit that detects load fluctuation of the motor at a time when the clamp part grips the paper bundle with the first wall portion and the second wall portion; and a thickness estimation unit that estimates a thickness of the paper bundle based on the load fluctuation, wherein the gripping release detection unit detects, based on the estimated thickness of the paper bundle, that the paper bundle is released from gripping of the clamp part.