To provide an envelope which can be effectively reused from one used in mailing a document or the like, expected to reduce wastes, and improve unsealing percentage of direct mail or the like, and its manufacturing method.

The envelope 10 has a pair of obverse and reverse sheets 2 and 3, and includes, on the pair of obverse and reverse sheets 2 and 3, a left side end 10a for coupling their left side rims, a right side end 10b for coupling their right side rims, a lower end 10d for coupling their lower end rims and an opening 10c between their upper end rims. Upper and lower separation lines 21a and 21b are formed inward from the opening 10c. Side separation lines 22a and 22b are formed to couple the upper and lower separation lines 21a and 21b with the lower end 10d between the lines 21a and 21b and the lower end 10d.