To provide a power supply noise reduction circuit and a power supply noise reduction method that do not require circuit elements to be increased in size and do not cause voltage drop in a power supply voltage. A power supply noise reduction circuit 10 that reduces noise included in a constant voltage output that is output from a power supply 2 to a load includes a first resistor 20 that is inserted into a power supply line L1 extending from the power supply 2 to the load, a filter 31 that is coupled to a load terminal of the first resistor 20 and outputs a first voltage that is obtained by reducing the noise from the constant voltage output, and a unity gain amplifier 32 that drives the first voltage output from the filter 31 and outputs the driven first voltage to the load terminal of the first resistor 20.