PURPOSE: To easily perform sampling even in a reacting process by constituting the title sampler so that shelf-type catalyst chambers are provided and a cover detachable quickly with one touch is made into a built-in heat insulator type, and a specified stopper is provided and furthermore gas seal is smoothly performed during operation.

CONSTITUTION: A cover 9 having a buit-in heat insulator 1 is provided to the upper part of a catalyst sampler 4. The cover 9 can be easily detached by extruding a hardware pressing it. Further catalyst 7 is packed in boxes fitted with knobs, and arranged on shelves 30 provided in the sampler 4. Furthermore the sampler 4 is prevented from being completely drawn out to the outer part by providing an end stopper. This sampler 4 is arranged to an arbitrary place in the catalytic layer 43 of a reactor 47. In case of performing sampling with this constitution, boxes are lifted up with a lifter via a lifting hardware 13 provided to the cover 9, and stopped at an arbitrary point and drawn out to perform sampling. In this case, the stopper is moved and fitted to a notched part and sealed with gas between frames 15 for fitting the cover.