To improve sealing capacity since grease inside the gear chamber is scraped up and is run out of ball bearings when a bevelled edge gear is formed in the output shaft of an electric motor in such power tools as a screw driver and others.

The sealing structure of the gear chamber attaches a seal member 21 to the output shaft 12 of the electric motor 11 inside the gear chamber 10 and by preparing a grease returning part 21a to the seal member 21, the grease is scraped up with the bevelled edge gear 12a and is blown forward by a centrifugal force in a radial oblique direction to prevent grease leakage from the ball bearing 20.