A scanning mechanism 6 moves an optical head 5 relative to a mount plate 2 in a scan direction, and light emitting diodes 3A, 3B mounted on the optical head 5 emit their respective beams of measurement light along the scan direction and onto two color regions TP3, TP3, respectively, of an immunochromatographic test strip mounted on the mount plate 2. Photodiodes 4A, 4B mounted on the optical head 5 receive respective beams of reflected light from the two color regions TP3, TP3 perpendicularly to colored lines on the immunochromatographic test strip, thereby implementing simultaneous measurement of color intensities of the colored lines formed in the two color regions TP3, TP3 of the immunochromatographic test strip.