A composite focused ion beam device has a sample stage for supporting a sample, a first ion beam irradiation system that irradiates a first ion beam for processing the sample, and a second ion beam irradiation system that irradiates a second ion beam for processing or observing the sample. The first ion beam irradiation system has a liquid metal ion source that generates first ions for forming the first ion beam. The second ion beam irradiation system has a gas field ion source that generates second ions for forming the second ion beam. The first ion beam irradiated by the first ion beam irradiation system has a first beam diameter and the second ion beam irradiated by the second ion beam irradiation system has a second beam diameter smaller than the first beam diameter. The first and second ion beam irradiation systems are disposed relative to the sample stage so that axes of the first and second ion beams are orthogonal to a tilt axis of the sample stage.