A signal output circuit includes a slope control circuit, a capacitor, a noise detector circuit and a fail-safe circuit. The slope control circuit charges and discharges the capacitor, the first terminal of which is connected to an output terminal, according to the control signal level, and drives transistors using the voltage of the second terminal of the capacitor, thereby controlling the slope of the output single. The noise detector circuit detects noise superimposed on the output terminal. When noise is detected, the fail-safe circuit performs a forced drive operation on the transistor to output the output signal at a level corresponding to the level of the control signal is output, regardless of the transistor being driven by the slope control circuit.