A lithium ion capacitor comprising, having stored within an outer casing: an electrode laminate obtained by laminating a negative electrode body in which a negative electrode active material layer including a carbon material as a negative electrode active material is placed on a negative electrode current collector; a separator comprising a polyolefin resin including a polyethylene; and a positive electrode body in which a positive electrode active material layer including a positive electrode active material comprising any of a carbon material or a carbon compound material is placed on a positive electrode current collector; and a non-aqueous electrolytic solution including a lithium ion-containing electrolyte, characterised in that, when said separator is maintained at 100°C over 1 hour in an unconstrained state, said separator has a thermal shrinkage of 3% to 10% in a first direction, and a thermal shrinkage of 2% to 10% in a second direction which is orthogonal to the first direction, and in that a larger electrode area which is any one of an area of the positive electrode active material layer of said positive electrode body or a negative electrode area of the negative electrode active material layer of said negative electrode body, and an area of said separator have a following relationship (separator area) > (electrode area); and wherein, X 1 and X 2 are both 0.5 to 8.0, wherein X 1 is calculated by the formula: X 1 = L 1 or L 1 ′ / A / 2 × 100 wherein, in an arbitrary straight line which is parallel to the first direction of said separator and makes any one of L 1 and L 1 ' the shortest, in a top view, A is a length of a portion where said electrode area in said arbitrary straight line and said separator overlap, and L 1 and L 1 ' are lengths of portions where said electrode area and said separator do not overlap; and wherein X 2 is calculated by the formula: X 2 = L 2 or L 2 ′ / B / 2 × 100 wherein, in an arbitrary straight line which is parallel to the second direction of said separator and makes any one of L 2 and L 2 ' the shortest, in a top view, B is a length of a portion where said electrode area in said arbitrary straight line and said separator overlap, and L 2 and L 2 ' are lengths of portions where said electrode area and said separator do not overlap. an electrode laminate obtained by laminating a negative electrode body in which a negative electrode active material layer including a carbon material as a negative electrode active material is placed on a negative electrode current collector; a separator comprising a polyolefin resin including a polyethylene; and a positive electrode body in which a positive electrode active material layer including a positive electrode active material comprising any of a carbon material or a carbon compound material is placed on a positive electrode current collector; and a negative electrode body in which a negative electrode active material layer including a carbon material as a negative electrode active material is placed on a negative electrode current collector; a separator comprising a polyolefin resin including a polyethylene; and a positive electrode body in which a positive electrode active material layer including a positive electrode active material comprising any of a carbon material or a carbon compound material is placed on a positive electrode current collector; and a non-aqueous electrolytic solution including a lithium ion-containing electrolyte, characterised in that, when said separator is maintained at 100°C over 1 hour in an unconstrained state, said separator has a thermal shrinkage of 3% to 10% in a first direction, and a thermal shrinkage of 2% to 10% in a second direction which is orthogonal to the first direction, and in that a larger electrode area which is any one of an area of the positive electrode active material layer of said positive electrode body or a negative electrode area of the negative electrode active material layer of said negative electrode body, and an area of said separator have a following relationship (separator area) > (electrode area); and wherein, X 1 and X 2 are both 0.5 to 8.0, wherein X 1 is calculated by the formula: X 1 = L 1 or L 1 ′ / A / 2 × 100 wherein, in an arbitrary straight line which is parallel to the first direction of said separator and makes any one of L 1 and L 1 ' the shortest, in a top view, A is a length of a portion where said electrode area in said arbitrary straight line and said separator overlap, and L 1 and L 1 ' are lengths of portions where said electrode area and said separator do not overlap; and wherein X 2 is calculated by the formula: X 2 = L 2 or L 2 ′ / B / 2 × 100 wherein, in an arbitrary straight line which is parallel to the second direction of said separator and makes any one of L 2 and L 2 ' the shortest, in a top view, B is a length of a portion where said electrode area in said arbitrary straight line and said separator overlap, and L 2 and L 2 ' are lengths of portions where said electrode area and said separator do not overlap.