To provide a prevention method of jitter capable of preventing the occurrence of jitter in a scanner simply at low cost.

This prevention method of jitter in a bidirectional scanning scanner is characterized by scanning by a laser beam 4 a sample 77 for reading timing determination fixed relatively to a sample stage and having a formed reference pattern, detecting photoelectrically light emitted from the sample for reading timing determination, to thereby generate digital data of the sample for reading timing determination, loading a sample 22 labeled by labeling material on the sample stage, scanning the sample by a laser beam, detecting photoelectrically light emitted from the labeling material, sampling digital data on even-numbered scanning line divisions of digital data of the sample acquired by digitization following sampling timing, to thereby generate the digital data of the sample.