1. A defect pixel detection apparatus comprising: an image sensor which includes an effective pixel configured to have a photoelectric conversion element and an output unit configured to output a pixel signal generated by the photoelectric conversion element, a first reference pixel configured to have the same pixel configuration as the effective pixel and be optically shielded, and a second reference pixel configured to have a pixel configuration different from that of the effective pixel; a defect level acquiring unit configured to acquire a defect level of a target pixel in the image sensor; and a defect pixel determination unit configured to determine whether the target pixel is a defect pixel by comparing a defect level of the target pixel with a defect detection threshold according to a type of the pixel.