1. A non-destructive testing method comprising: irradiating an object to be tested with a line-formed light forming a rectilinear optical line, said rectilinear optical line having a length sufficient to cover at least a portion of the object; relatively scanning said rectilinear optical line over said object to be tested in a first direction intersecting said optical line to obtain a first one-dimensional image; and relatively scanning said rectilinear optical line over said object to be tested in a second direction intersecting said first direction to obtain a second one-dimensional image, wherein said first and second one-dimensional images are obtained by a scanning laser Superconducting Quantum Interference Devices (SQUID) method in which a plurality of SQUID elements are arrayed in a line, provided that said rectilinear optical line and said plurality of SQUID elements arrayed in the line are fixed so that they vertically overlap each other along a longitudinal direction of said rectilinear optical line.