A circuit board is provided in which tamper resistance is improved by making probing by third parties difficult, while solving problems associated with the current techniques and manufacturing costs. A signal line through which a confidential signal requiring tamper resistance flows and components 32 and 33 connected to the signal line 21 by the terminals thereof, are laid out in a component-containing layer 13 of a circuit board 10. Only a confidential signal having been encrypted through a predetermined component 31 is outputted to an observation point 34 provided on a surface of the circuit board 10. External observation and control of the confidential signal is performed by decoding a cipher provided by the component 31 to the signal which appears at the observation point 34.