It's a pretty piece, and rather unusual - I haven't seen anything like this either. The garter fittings are similar to a '20s corset that I have, that I thought was Edwardian until I researched it more, but yours has too much shape to be '20s: is it clipped to the mannequin perhaps? If the hour glass shape is authentic I think it's either a '20s piece that was updated in a curvier era or a '30s piece that uses old styled materials.
If you were able to determine the fabric composition it might help: a rayon is more likely to be a '30s piece although they did use rayon in '20s lingerie.