A signal processing apparatus includes an acquisition unit that acquires input data and detection target data, a noise strength setting unit that sets a noise strength K used to a predetermined stochastic resonance processing and a stochastic resonance processing unit that performs the predetermined stochastic resonance processing and outputs processed data. The predetermined stochastic resonance processing is a processing based on a formula in which processed data J(x) is represented by I(x), the noise strength K and the threshold value T and the processed data J(x) corresponds to a result in a case where M is infinite in the following formula, J ⁡ ( x ) = 1 M ⁢ ∑ m = 1 M ⁢ j ⁡ ( x , m ) . The noise strength setting unit sets the noise strength based on a function of a correlation coefficient between the result of the predetermined stochastic resonance processing and the detection target data and the noise strength K.