An solid-state image pickup apparatus compensates for deterioration in horizontal transfer efficiency conspicuous in an image captured in, e.g. a high ISO sensitivity mode. A horizontal transfer efficiency calculator in a transfer efficiency compensator of a signal processor calculates in advance a local horizontal transfer efficiency for signal charge transfer in a concentrating portion of an image sensor, for each value of ISO sensitivity, to store a resultant value. The signal processor processes a digital image signal representing a photographed subject. In main shooting with a value of ISO sensitivity for image pickup set, a subject field is captured, and a horizontal transfer efficiency detector detects a local horizontal transfer efficiency consistent with the value of ISO sensitivity for image pickup. A horizontal transfer efficiency corrector corrects a digital image signal based on the consistent local horizontal transfer efficiency.