A ferrite clamp includes a pair of divided cores, each being formed in an open circular shape; and a pair of case parts, each being adapted to hold each of the divided cores. When the case parts are assembled with each other, the pair of divided cores held by the case parts constitute a circular magnetic core having an insertion hole to insert an electric cable therethrough. The case part includes, in a portion thereof to hold an outer peripheral surface of the divided core, a protruding portion which is outwardly convex.