An image processing apparatus for reducing a blur in an input image, said image processing apparatus comprising: a noise processing unit configured to perform noise processing that reduces noise to the input image, to generate a noise-processed image; wherein the noise processing unit comprises: a noise reduction unit configured to perform noise reduction processing to the input image in a spatial domain to generate a noise-reduced image; a first fluctuation range setting unit configured to set a first fluctuation range that decreases as the frequency increases, and a frequency restriction unit configured to modify, in the frequency domain, the noise-reduced image to generate the noise-processed image such that a variation indicating a magnitude of the degree of variation does not exceed the first fluctuation range; and in that the image processing apparatus further comprises a restoration processing unit configured to perform image restoration processing that reduces a blur to the noise-processed image by using a restoration function indicating a degree of restoration at each frequency in the frequency domain, wherein said noise processing unit is configured to perform the noise processing such that the degree of variation of the noise-processed image from the input image in a frequency domain is restricted by said frequency restriction unit according to the degree of restoration indicated by the restoration function and performed by said restoration processing unit, wherein said noise processing unit is configured to perform the noise processing such that the degree of variation at the frequency becomes more restricted as the degree of restoration at the frequency increases. a noise processing unit configured to perform noise processing that reduces noise to the input image, to generate a noise-processed image; wherein the noise processing unit comprises: a noise reduction unit configured to perform noise reduction processing to the input image in a spatial domain to generate a noise-reduced image; a first fluctuation range setting unit configured to set a first fluctuation range that decreases as the frequency increases, and a frequency restriction unit configured to modify, in the frequency domain, the noise-reduced image to generate the noise-processed image such that a variation indicating a magnitude of the degree of variation does not exceed the first fluctuation range; and in that the image processing apparatus further comprises a noise reduction unit configured to perform noise reduction processing to the input image in a spatial domain to generate a noise-reduced image; a first fluctuation range setting unit configured to set a first fluctuation range that decreases as the frequency increases, and a frequency restriction unit configured to modify, in the frequency domain, the noise-reduced image to generate the noise-processed image such that a variation indicating a magnitude of the degree of variation does not exceed the first fluctuation range; and in that the image processing apparatus further comprises a restoration processing unit configured to perform image restoration processing that reduces a blur to the noise-processed image by using a restoration function indicating a degree of restoration at each frequency in the frequency domain, wherein said noise processing unit is configured to perform the noise processing such that the degree of variation of the noise-processed image from the input image in a frequency domain is restricted by said frequency restriction unit according to the degree of restoration indicated by the restoration function and performed by said restoration processing unit, wherein said noise processing unit is configured to perform the noise processing such that the degree of variation at the frequency becomes more restricted as the degree of restoration at the frequency increases.