To prevent the lowering of the performance of an infrared ray detector by capturing the outgas and contaminant generated by a artificial satellite itself by a cold trap, and preventing the invasion of the contaminant from an external to the artificial satellite by the cold trap.

When a heating state of a baking heater is stopped, and an infrared ray detector 11 starts its operation again, the outgas is attached to the cooled infrared ray detector 11 with a lapse of time. On this occasion, the outgas which is generated in the overheating by the baking heater, and is not discharged to an external, is actively adsorbed by the cold trap 31 cooled by a radiational cooling plate 32. Further the contaminant counter-flowed from an exhaust port 34 can be also adsorbed by the cold trap 31. According the outgas and the contaminant adsorbed by the cold trap 31 are kept at a low temperature at all times, so that the scattering thereof can be prevented.