Sealing sheet

The present invention provides a sealing sheet containing a flame retardant adhesive sheet having a flame retardant-containing adhesive layer, which has a retention time of 60 - 2000 seconds in the following constant load peel test: [constant load peel test] (1) a sealing sheet is cut into a 10 mm width x 50 mm length tape, (2) the tape is laid on a duralumin panel, a 5 kgf roller is run on the tape from one end of the tape to the other end of the tape in the length direction thereof to press the tape against the duralumin panel to form a sample, and (3) the sample is left standing at ambient temperature, normal humidity for 24 hr, the sample is fixed horizontally with the tape side facing downward, a 30 gf plummet is hung at one end in the tape length direction, the time from hanging the plummet to reaching a tape peel distance of 30 mm is measured, and this time is taken as the retention time.