The invention relates to an unstacker device for unstacking flat articles, said unstacker device including: first detection means for detecting transitions between article types; at least first and second specialized unstacking programs and a default unstacking program, which programs are suitable for maintaining respectively a first nominal gap, a second nominal gap, and a default nominal gap, between two consecutive flat articles; and a monitoring/control unit arranged for automatically executing said default unstacking program in response to detection of said transition, for counting said flat articles subsequent to said transition, and, in response to a predetermined counting threshold being reached, for executing, for said subsequent flat articles and until the next transition detection, the corresponding one of said first and second specialized unstacking programs. The invention also relates to a method of unstacking flat articles using said unstacker device.