To support a sealing work so as to be performed easily and correctly.

A supporting device for envelope sealing work 100 includes a couple of cutter blades 101 which have blade parts and arranged at a predetermined distance with the cutter parts directed to the front side of an operator, a holding member 102 which holds an adhesive tape 106 so that the adhesive tape 106 with the adhesive surface directed to the front side may be laid across a couple of cutter blades 101, an envelope support member 103 which is placed on the side away from an operator rather than the adhesive tape 106 held by the holding member 102 and supporting the envelope to be sealed through the adhesive tape 106, a guide member 104 for guiding the position of envelope against the envelope support member 103, and a moving mechanism 105 for making the envelope support member 103 move to the separated side from the front side according to the external force when an external force effecting on the separated side from the front side against the envelope support member 103 is applied.