An image sensing apparatus including a light source, an image sensor, at least one lens, and a wavelength selecting device is provided. The light source is configured to emit an illumination light to irradiate an object. The image sensor is configured to receive a light signal from the object and send an image signal corresponding to the light signal. The at least one lens is located on a transmission path of the light signal and between the object and the image sensor. The wavelength selecting device is located on the transmission path of the light signal and between the object and the image sensor. The wavelength selecting device has a first reflector and a second reflector, and a gap exists between the first reflector and the second reflector. The gap is adapted to be adjusted to have a first predetermined optical path length or a second predetermined optical path length.