The perpetrator struck and injured the 60-year-old female employee with his handgun, but apparently lost his nerve and ran off without any money.
The clown struck at 5:25 am, just as the store clerk was unlocking the doors for the morning. He spoke German with a foreign accent, threatening her from behind with his gun, then striking her in the face with the weapon.
The victim was taken to hospital for treatment. Police are searching for a man 1.70 metres tall, dressed in dark clothing and carrying a dark backpack.
The Upper Austria chamber of commerce has offered a reward of €1,000 for information leading to a conviction of the robber.