To stably perform transmission of a signal with high reliability without being subjected to thermal influence, when a magnetic signal transmitter performs, in noncontact, transmission of a signal between a plurality of electric circuits electrically insulated from one another, and mount the transmitter easily on a circuit board, with a simple and small structure.

An electric signal transmitter is constituted such that it detects, in noncontact, the change of the current flowing in the signal line in a first electrical circuit system by means of a magnetoresistive effect element, and that it transmits a signal to a second electric circuit system in the condition that they are electrically insulated from each other, by the change in the resistance of the magnetic resistance effect element at that time.