A reactor includes a laminated core formed by laminating soft-magnetic ribbons in a lamination direction. The laminated core has a gap formed across a magnetic path direction in the laminated core. The laminated core also has a flat facing surface that faces the gap and a pair of flat side surfaces that are respectively on opposite sides of the facing surface in the lamination direction. The laminated core further has a pair of first corner curved surfaces that are formed between the facing surface and the pair of side surfaces. Each of the first corner curved surfaces has a width in the lamination direction greater than the thickness of each of the soft-magnetic ribbons. For each of the first corner curved surfaces, a length of the first corner curved surface in the magnetic path direction is greater than the width of the first corner curved surface in the lamination direction.