Provided is a current sensor capable of being assembled even if a bus bar inserted through a magnetic core has a complex shape that is difficult to insert through an opening portion of a case. A case includes a first case segment and a second case segment provided with opening portions having a cut-out shape that is open toward a direction orthogonal to a direction in which a detection target portion of a bus bar extends, and the case is assembled to the detection target portion by inserting the detection target portion into the opening portions from the direction orthogonal to the direction in which the detection target portion extends.