A signal processing apparatus (100, 200, 300) comprising: an adder (110, 210, 310) arranged to acquire a plurality of input signals from a plurality of microphones (10a, 10b) and calculate an added value obtained by adding the input signals together; a subtracter (120, 220, 320) arranged to acquire a plurality of input signals from the plurality of microphones (10a, 10b) and calculate a subtracted value obtained by subtracting one input signal from the other input signal; a first power calculator (130a; 230a; 330a) arranged to calculate a first power by summing up squared values of the added value; a second power calculator (130b; 230b; 330b) arranged to calculate a second power by summing up squared values of the subtracted value; a determination unit (150, 250, 350) arranged to determine that noise is included in the input signals when a difference between the first power and the second power is smaller than a threshold value; a gain calculator (160, 260, 360) arranged to calculate a gain based on the added value and the subtracted value, wherein, when the determination unit (150, 250, 350) determines that noise is included in the input signals, the gain calculator (160, 260, 360) is arranged to: calculate the gain by calculating a ratio as the second power divided by the first power, and subtracting the calculated ratio from 1; when the calculated gain is greater than or equal to a predetermined gain, output the calculated gain; and when the calculated gain is smaller than the predetermined gain, output the predetermined gain; and a noise suppression unit (170, 270, 370) arranged to suppress noise of the input signals by multiplying the input signals by the gain output by the gain calculator (160, 260, 360). an adder (110, 210, 310) arranged to acquire a plurality of input signals from a plurality of microphones (10a, 10b) and calculate an added value obtained by adding the input signals together; a subtracter (120, 220, 320) arranged to acquire a plurality of input signals from the plurality of microphones (10a, 10b) and calculate a subtracted value obtained by subtracting one input signal from the other input signal; a first power calculator (130a; 230a; 330a) arranged to calculate a first power by summing up squared values of the added value; a second power calculator (130b; 230b; 330b) arranged to calculate a second power by summing up squared values of the subtracted value; a determination unit (150, 250, 350) arranged to determine that noise is included in the input signals when a difference between the first power and the second power is smaller than a threshold value; a gain calculator (160, 260, 360) arranged to calculate a gain based on the added value and the subtracted value, wherein, when the determination unit (150, 250, 350) determines that noise is included in the input signals, the gain calculator (160, 260, 360) is arranged to: calculate the gain by calculating a ratio as the second power divided by the first power, and subtracting the calculated ratio from 1; when the calculated gain is greater than or equal to a predetermined gain, output the calculated gain; and when the calculated gain is smaller than the predetermined gain, output the predetermined gain; and calculate the gain by calculating a ratio as the second power divided by the first power, and subtracting the calculated ratio from 1; when the calculated gain is greater than or equal to a predetermined gain, output the calculated gain; and when the calculated gain is smaller than the predetermined gain, output the predetermined gain; and a noise suppression unit (170, 270, 370) arranged to suppress noise of the input signals by multiplying the input signals by the gain output by the gain calculator (160, 260, 360).