An image signal processing apparatus includes: a solid-state image pickup device capable of taking a two-dimensional image, the device having a plurality of primary transfer paths and a secondary transfer path, wherein the plurality of primary first transfer each have a plurality of transfer stages each capable of storing electric charges and transfer the electric charges in a first direction, and the secondary transfer path has a plurality of transfer stages each capable of storing electric charges, receives electric charges in the plurality of primary transfer paths, and transfers the electric charges in a second direction; a reading unit for scanning the two-dimensional image on the solid-state image pickup device in a main scan direction corresponding to the second direction and in a sub-scan direction corresponding to the first direction and reading the electric charges in the secondary-transfer path as image signals; and an output unit for outputting the read image signals on a monitor by interchanging the main scan direction and the sub-scan direction.