An illumination device including a laser light source, a first wavelength selective element, and a wavelength conversion element is provided. The laser light source provides a laser beam. The first wavelength selective element has different transmittances for the laser beam incident at different angles. In a first mode of the illumination device, the laser beam is incident on the first wavelength selective element at a first angle, and the laser beam is reflected by the first wavelength selective element. In a second mode of the illumination device, the laser beam is incident on the first wavelength selective element at a second angle greater than the first angle, and the laser beam penetrates the first wavelength selective element. The wavelength conversion element converts the laser beam into a first converted light beam. A projection device using the illumination device is also provided.