A laser pulse train jitter measuring device includes a first optical path having a length set at a first value or a second value and a second optical path having a length variable between a first value and a second value. A laser beam is split into a first beam directed to the first optical path and a second beam directed to the second optical path. The split beams are recombined into a correlated beam and recorded as visible images so that jitter in the laser beam can be detected from the differences in the recordings when the first optical path has its first length while the second optical path is varied between the first value and the second value from when the first optical path has its second length while the second optical path is varied between the first value and the second value.