An electric current detector which is mountable on a circuit board on which there is mounted a fluxgate-type magnetic sensor IC chip which detects magnetic flux for electric current detection, including: a substantially ring-shaped core which forms a magnetic-path for magnetic flux induced by detection-target electric current, wherein the core includes a gap which is arranged to become substantially parallel with respect to the circuit board when mounting the aforesaid electric current detector on the circuit board and which is at a place positioned on or on the upper side of the magnetic sensor IC chip in the magnetic-path when mounting the aforesaid electric current detector on the circuit board.