1. An image pickup apparatus comprising: an image pickup unit that converts an optical image of an object received via an imaging lens into an image signal; an exposure control unit capable of controlling an exposure time of the image pickup unit such that the object image is underexposed relative to an appropriate exposure; an image processing unit that generates a display image signal by implementing predetermined dynamic range expansion processing on an image signal obtained by performing underexposed image pickup; a warning region detection unit that detects an image region in which a pixel within a predetermined gradation range exists as a warning region from the image signal either prior to implementation of the predetermined dynamic range expansion processing or following implementation of the predetermined dynamic range expansion processing; a synthesis unit that synthesizes the display image signal generated by the image processing unit with a warning pattern corresponding to the warning region detected by the warning region detection unit; and a display unit that displays the image synthesized by the synthesis unit as a live view image.