A tilted illumination observation method and observation device with easy adjustment, high speed, good reproducibility and low cost is provided. A high resolution tilt image of a specimen is obtained by extracting the blurring on the scanning spot occurring during beam tilt from the image (step 6) captured by the tilted beam, and the image (step 4) captured from directly above the standard specimen; and then deconvoluting (step 11, 12) the tilted image of the target specimen (step 10) using the extracted scanning spot from the oblique beam.