To reduce noise signal due to external magnetic field effectively upon transmitting a signal from a circuit of one side to the circuit of the other side through a magnetic field under electrically insulated condition.

The signal transmitting device 100 is equipped with a pair of transformers 20, 40. The input side coils 22, 42 of the pair of transformers are arranged in a relation that a magnetic field is generated in a direction spatially reverse to the input signal. The output side coils 24, 44 of the pair of transformers are arranged in a relation to output induction current of the same polarity with respect to the magnetic field of the same direction. An induction current due to the input signal is outputted from respective output coils 24, 44 as the induction current of opposite polarity mutually. Induction current due to the external noise is outputted as the induction currents having the same polarity from respective output coils 24, 44. When a difference is obtained between the induction currents outputted from the output coils 24, 44, signal components due to the noise are canceled out whereby a signal can be obtained in which the signal component due to the input signal is doubled. An S/N ratio can be made high upon transmitting signal.

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