What kind of longhorn beetle is this?
Rosalia alpina (common name: Rosalia longicorn)

See here: Rosalia longicorn

The link I added shows a picture of an identical Alpine Longhorn Beetle. This longhorn beetle occurs mainly in the European Alps and the neighboring countries (e.g. Germany, Hungary, and France). Minimum height is around 700m above sea level. The adults are active from June to September. The color varies between blue and grey, the head is characterized by one spine on each side of the head. The number of black dots on the elytra varies.