in the inner end of the container 4 is in the form of a threaded hole 4 39 a and a screw 9 is screwed into the threaded hole 4 39 a in place of the permeable porous resin film 6 in the aforementioned embodiment in this case a spring washer 10 is provided with this arrangement the interior of the lamp interior of the reflector 1 and the interior of the container 4 are in communication with each other through a clearance between the threaded hole 4 39 a and the screw 9 and through an extremely elongated passage in the form of a slit of the spring washer 10 to assume a vented state for this reason the amount of air moving in and out of the lamp when the latter is lighted and unlighted is the maximum after a fixed period of time and thereafter gradually reduces that is the flow of air continues for a long period of time accordingly when the lamp is being lit the water content released from the drying agent 8 is discharged outside over a long period of time and the remaining water content is not left within the container 4 on the other hand when the light is unlighted the flowing in open air contacts with the low temperature drying agent 8 for a long period of time and dehumidifying thereof is satisfactorily carried out in the prior.