The purpose of the present invention is to provide an overlay error measuring device which measures an overlay error with high accuracy even when a lower layer pattern is disposed under a thin film and a sufficient signal amount cannot be ensured. The present invention proposes an overlay error measuring device provided with an arithmetic processing unit for measuring a pattern formed on a sample on the basis of a signal waveform obtained by a charged particle beam device. The arithmetic processing unit finds a correlation with the signal waveform using a partial waveform obtained on the basis of partial extraction of the signal waveform, forms a correlation profile indicating the correlation, and measures an overlay error using the correlation profile.