Abstract: The present invention relates to a laser apparatus comprising a laser light emitting optical system for emitting laser light to a surface, a power stabilizing system for stabilizing the laser light power with a predetermined power interval, and a deflection system for deflecting light reflected from the surface away from the power stabilizing system. Thereby, the power stabilizing system will not erroneously regulate the power due to reflections from the surface to be treated. Furthermore, the invention relates to a method for treating an animal, including a human being, for a laser light treatable disease using the laser apparatus on the skin or the mucosa of the animal and allowing laser light to be emitted from the laser light emitting optical system to the skin or mucosa.