PURPOSE: To enable the securing of waterproofing at a housing through part of a drive element.

CONSTITUTION: This waterproof structure provides for a part where a housing 4 is pierced by a drive element 6 which converts rotary motion to reciprocation to make an inner blade 13 reciprocate. An adhesion part with the drive element 6 in a waterproof rubber 27, an inner periphery of which is tight on the external surface of the drive element 6 while the periphery thereof is fixed on a housing 1 is covered with a protective wall 9 provided on the inner blade 13. This prevents a rapid water flow from hitting the adhesion part directly between the waterproof rubber and the drive element.