According to the pixiv title/google, it's a Theorbo. https://en.wikipedia.org/wiki/Theorbo

qazmlpok said:

According to the pixiv title/google, it's a Theorbo. https://en.wikipedia.org/wiki/Theorbo

Thanks for that, mate ;)

Based on A Woman Playing the Theorbo-Lute and a Cavalier by Gerard ter Borch the Younger. (Who seems to have done a number of pictures with some combination of that instrument, that tablecloth and those pilasters, but I think this is the right one.)