A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at one end of the two-ply sheet. The sheet separation device includes a separator that includes a first separator and a second separator. The first separator is inserted into a gap between the two sheets of the two-ply sheet. The second separator is inserted between the two sheets at said another end of the two-ply sheet that is opposite to the one end of the two-ply sheet and moves in a width direction of the two-ply sheet after the first separator is inserted into the gap and relatively moves from the one end to said another end.