An observation apparatus which observes inside of an observed object is composed to: a light source (26) for emitting light an insertion module (12), which includes a light-source light emitting module (22) around its distal end, for being inserted into inside of the observed object, the light-source light emitting module emitting light from the light source an imager member (24), which is provided close to the distal end of the insertion module, for detecting a light quantity of incident visible light a determination module (30) for performing determination relating to a position of a distal end of the insertion module and a controller (28) for controlling the light source such that a null signal is transmitted from the light-source light emitting module, the null signal being characteristic for detection of the position of the distal end of the insertion module and obtained by making at least light of a predetermined wavelength region have an absence of visible light. The imager member performs detecting operation in a period in which the null signal is transmitted, and outputs detection information indicating a detection result, and the determination module performs the determination relating to the position of the distal end of the insertion module, based on the detection information outputted by the imager member.
