A spatial frequency reproducing method, the method comprising: modulating, by a first means, a coherent light emitted from a light source into two lights which have frequencies different from each other and are irradiated separately to be partially overlapped with each other; two-dimensionally scanning the two lights by a second means; irradiating an object under measurement with the two lights which are scanned by a third means; receiving and converting into, by a fourth means (29, 49), an electrical signal with two or more divided photo detectors (29D, 29E, 49D, 49E), respectively, lights from the object under measurement with a boundary line being interposed therebetween in a direction substantially perpendicular to the direction in which the two lights are separated; characterized in that the method further comprises: amplifying, by a fifth means, respective electrical signals photoelectrically converted by the divided photo detectors (29D, 29E, 49D, 49E) of the fourth means (29, 49) with respect to respective areas with the boundary line being interposed therebetween while varying a degree of amplification according to frequencies of the electrical signals to increase the degree of amplification in a band where a spatial frequency is high and generating a difference signal or a summation signal of the amplified signals; and obtaining a phase difference or an intensity difference of the difference signal or the summation signal by a sixth means to obtain a measurement value. modulating, by a first means, a coherent light emitted from a light source into two lights which have frequencies different from each other and are irradiated separately to be partially overlapped with each other; two-dimensionally scanning the two lights by a second means; irradiating an object under measurement with the two lights which are scanned by a third means; receiving and converting into, by a fourth means (29, 49), an electrical signal with two or more divided photo detectors (29D, 29E, 49D, 49E), respectively, lights from the object under measurement with a boundary line being interposed therebetween in a direction substantially perpendicular to the direction in which the two lights are separated; characterized in that the method further comprises: amplifying, by a fifth means, respective electrical signals photoelectrically converted by the divided photo detectors (29D, 29E, 49D, 49E) of the fourth means (29, 49) with respect to respective areas with the boundary line being interposed therebetween while varying a degree of amplification according to frequencies of the electrical signals to increase the degree of amplification in a band where a spatial frequency is high and generating a difference signal or a summation signal of the amplified signals; and obtaining a phase difference or an intensity difference of the difference signal or the summation signal by a sixth means to obtain a measurement value. amplifying, by a fifth means, respective electrical signals photoelectrically converted by the divided photo detectors (29D, 29E, 49D, 49E) of the fourth means (29, 49) with respect to respective areas with the boundary line being interposed therebetween while varying a degree of amplification according to frequencies of the electrical signals to increase the degree of amplification in a band where a spatial frequency is high and generating a difference signal or a summation signal of the amplified signals; and obtaining a phase difference or an intensity difference of the difference signal or the summation signal by a sixth means to obtain a measurement value.