An image signal processing apparatus includes a hard disk. The hard disk is as necessary created with a directory to which time information according to a time counter is assigned. An image file is stored in a latest directory having the latest creation time among a plurality of directories thus created. When a time indicated by the time counter is modified retroactive to the past, a marker is added to a directory having the time information according to the time counter before being modified. The latest directory is detected on the basis of the marker and the time information.