To provide a variable attenuation circuit strong against variation having linear attenuation control characteristics and excellent noise characteristics on an Si substrate.

The variable attenuation circuit has a signal attenuation part 400 having a MOSFET 411 for variable attenuation in serial with a signal line connecting a signal input terminal 404 with a signal output terminal 405, an attenuation amount control circuit part 401 which controls gate potential of the MOSFET 411 for variable attenuation to adjust an attenuation amount and a source bias circuit part 402 for providing the MOSFET 411 for variable attenuation with a source bias. The source bias circuit part 402 has a MOSFET for bias and source potential of the MOSFET for bias is provided to source potential of the MOSFET for attenuation. In addition, a resistor 424 is added between a back gate and a substrate of the MOSFET 411 for variable attenuation, capacity 403 is added between a gate and an earth terminal and capacity 425 and a switch 426 are added between the source bias circuit part and the earth terminal.