PURPOSE: To provide the bonding method of waterproof sheets or waterproof cloths to be bonded without rising the surface temperature and without giving damage to the waterproof sheets and waterproof cloths and increasing the bonding strength.

CONSTITUTION: Welding materials 3 and 4 are disposed together with a conductive body 5 between the bonding faces of the ends of two waterproof sheets 1 and 2 or waterproof cloths, and the conductive body 5 is heated by electromagnetic induction to melt heat welding materials 3 and 4 and mutually bond the ends. The ends of two waterproof sheets or waterproof cloths are overlapped and bonded in this method, and bonding can be carried out without using a solvent or a bonding agent, and nasty smell is not generated.