PURPOSE: To photograph and record the generation process and the combustion process of a fuel mist according to a series of sequences by a fluorescent exciation operation by providing an observation probe, a camera, an optical means, a control device and a laser for irradiation.

CONSTITUTION: First, a combustion explosion is suppressed temporarily with reference to a cylinder as an observation object, a pulse beam which excites fluorescence at a plurality of timings at proper intervals is irradiated 14 during one cycle of an internal combustion engine 1 to be observed, and the beam is observed 2 and photographed 4, 7, 6. Then, a fuel passage or an ignition circuit is connected, an ordinary fuel explosion is performed, and the state of a spontaneous light emission is observed 2 and photographed 4, 7, 8. Then a series of photographing operations is completed, a synchronization control circuit 10 rearranges photographed results due to irradiation with excitation light and photographed results by the spontaneous light emission in the order of phase timings in one cycle. Then, they are stored 20 as sequence information in order to rearrange them in the order of rotational phases, and they are displayed 30a. Thereby, the front and rear relationship of phases inside one cycle of the photographed results can be displayed so as to be understood easily and without any error.