To provide a signal amplifier which does not require the inserting/pulling out of a power plug and does not cause useless power consumption when a personal computer is not used.

A signal amplifier 20 includes an amplifier 21a for amplifying television signals and is constituted so as to output television signals amplified by the amplifier 21a to a personal computer with a television function and receive power for the amplifier 21a from a general interface of the personal computer with the television function. Since the power of the amplifier 21a is secured by DC voltage received from the general interface of the personal computer with the television function, the power of the amplifier 21a is also turned on/off in interlocking with the ON/OFF of the power supply of the personal computer with the television function.