Today there's no real difference between Spelmansmusik and Swedish folk music. During the middle ages in the agrarian society in Sweden, people who played music called "bruksmusik" were Spelmän. The bruksmusik was mostly played for dancing and sometimes for weddings and big festive ceremonies. Basically, they played dance rhythm music like polska, polka, schottis and waltz. Today, these kind of men call themselves "folkmusiker", and the word Spelman is used only to mark one's special belonging to a section or a group. So, Leif Alpsjö, for instance, is a folkmusiker, calling himself a Spelman, because Spelman is a special traditional word. And then there is a special prize in Sweden if you want to become a "real" Spelman called "Riksspelman". You will earn that prize if you play Swedish folk music extraordinary skillfully in the Swedish dancing arena called "Svenska Folkdansringen".
The instrument you have seen is KANTELE. It is our national instrument... In our national epos Kalevala, which you can read even in Japanese or English kantele is meant many times... )