An electric stapler (1A, 1B, 1C, 1D, 1E) comprising: a binding part configured to bind a sheet bundle by striking out a staple having a crown portion and leg portions; and a first guide part configured to guide the sheet bundle to the binding part, and a second guide part facing the first guide part, wherein the first guide part and the second guide part face each other at a distance equal to or greater than a thickness of a sheet bundle where a maximum number of bindable sheets capable of being bound by the staple are stacked, wherein the first guide part and the second guide part are opened therebetween as both sides along a length direction of the crown portion of the staple, which is struck out by the binding part, and one side away from the binding part along a direction orthogonal to the length direction of the crown portion are coupled each other, and wherein lengths from end portions on one side, which are away from the binding part along the direction orthogonal to the length direction of the crown portion, of the first guide part and the second guide part to the binding part are 15mm or longer, and wherein at least one of the first guide part and the second guide part has a restraint portion for restraining a number of sheets that are inserted between the first guide part and the second guide part, characterized in that at least one of the first guide part and the second guide part has a first relief portion having a shape that is concave with respect to the restraint portion and has a dimension equal to or greater than a thickness of the staple, and enabling the staple that has bound the sheet bundle to pass therethrough. a binding part configured to bind a sheet bundle by striking out a staple having a crown portion and leg portions; and a first guide part configured to guide the sheet bundle to the binding part, and a second guide part facing the first guide part, wherein the first guide part and the second guide part face each other at a distance equal to or greater than a thickness of a sheet bundle where a maximum number of bindable sheets capable of being bound by the staple are stacked, wherein the first guide part and the second guide part are opened therebetween as both sides along a length direction of the crown portion of the staple, which is struck out by the binding part, and one side away from the binding part along a direction orthogonal to the length direction of the crown portion are coupled each other, and wherein lengths from end portions on one side, which are away from the binding part along the direction orthogonal to the length direction of the crown portion, of the first guide part and the second guide part to the binding part are 15mm or longer, and wherein at least one of the first guide part and the second guide part has a restraint portion for restraining a number of sheets that are inserted between the first guide part and the second guide part, characterized in that at least one of the first guide part and the second guide part has a first relief portion having a shape that is concave with respect to the restraint portion and has a dimension equal to or greater than a thickness of the staple, and enabling the staple that has bound the sheet bundle to pass therethrough.