A semiconductor device includes: a first power source (PS1) pad supplied with a PS1 voltage; a PS1 line connected to the PS1 pad; a first ground line (G1); an output circuit operated using the PS1 voltage; a second power source (PS2) pad supplied with a PS2 voltage; a PS2 line connected to the PS2 pad; a second ground line (G2); a signal line connected to an output end of the output circuit; an input circuit connected to the signal line at an input end receiving a signal from the output end and operated using the PS2 voltage; a main protection circuit unit providing discharge routes between the PS1 pad and G1, G1 and G2, and G2 and the PS2 pad; and a sub protection circuit unit. The output circuit includes: a circuit element arranged between the PS1 line and the signal line and able to function as a resistive element.