To enable detection of occurrence of abnormality in a more preferable manner when the abnormality occurs in signal processing applied to pixel signals. A signal processing device including: a signal processing unit that performs signal processing on pixel signals; and a data generation unit that associates first test data based on first processing, second test data based on second processing, and valid data obtained by performing the second processing on the pixel signals corresponding to a second frame after a first frame to generate frame data corresponding to the second frame, in which, the first processing is the signal processing for generating the valid data in the first frame; the second processing is the signal processing for generating the valid data in the second frame; and presence or absence of abnormality in the signal processing is diagnosed on the basis of the first test data associated with the frame data corresponding to the first frame, and the first test data associated with the frame data corresponding to the second frame.