To eliminate a problem of processing accuracy (detecting accuracy) being influenced by a deterioration in insulation with time, and enhance certainty and reliability in detection of a break.

A signal output portion 2so of a first signal processing unit 2 which outputs signals Sd which vary within a predetermined range A, and a signal input portion 3si of a second signal processing unit 3 which is fed with the signals Sd, are connected with each other through a signal line Ls. Further, the signal input portion 3si and the power output portion 3po of the second signal processing unit 3 are connected with each other through a pull-up resistor Ru to form a signal processor M. When an anomaly detection circuit 1 for detecting a break in the signal line Ls and power lines Lp and Ln is constituted in the signal processor M, an active element 4 is connected in series with the signal line Ls in the first signal processing unit 2. The active element 4 is turned on when supplied with the supply voltage E (Et) of the power line Lp in the first signal processing unit 2, and off when the supply of the supply voltage E (Et) is removed.