This clamp-type ammeter has a flexible substrate of which an inner wall is configured to be able to deform into a substantially cylindrical shape. The clamp-type ammeter has a plurality of magnetic sensor elements disposed at the inner wall of the flexible substrate. The clamp-type ammeter has a tube of which one end is connected to the flexible substrate. The clamp-type ammeter has an operation unit that is connected to the other end of the tube and that can operate the deformation of the flexible substrate.