An optical system that obtains characteristics of a transmission path in atmosphere, when laser light propagates through this transmission path, at a place separated from this transmission path and before the propagation, and corrects wavefront of the laser light based on the obtained characteristics, is provided. The optical system is provided with an irradiation device and an atmospheric characteristics obtaining system. The irradiation device irradiates an external target with light via a first optical path. The atmospheric characteristics obtaining system is arranged in a second optical path separated from the first optical path and obtains characteristics of atmospheric environment in the first optical path with respect to the irradiated light. The irradiation device is provided with wavefront correction optics. The wavefront correction optics correct wavefront of the irradiated light based on the obtained characteristics.