To provide a sheet postprocessing device and an image forming system having the same, for attaining folding without having a complicated mechanism, without enlarging the device, without largely changing a device constitution status quo.

This sheet postprocessing device has a folding processing mechanism having a folding plate 74 arranged so as to be capable of advancing-retreating in the substantially vertical direction to the paper carrying direction, and a pair of unabutting reciprocal folding roller pairs 81 arranged in its advancing direction and folding a sheet or a sheet bundle pushed in a nip by the folding plate 74. The respective folding rollers 81a and 81b for forming the folding roller pairs 81 are independently driven.