A seal structure for an electric device having an electrically conductive lead portion which passes through a through hole in a bottom surface of an electrically insulating housing. Additionally, the housing is provided with a lateral slot in a side surface thereof which is in communication with the through hole and which is filled with a sealant. Thus, the sealant which has been filled into the lateral slot adheres to the surface of the terminal piece exposed in the interior of the lateral slot and is solidified therein. Therefore, when this electric device is mounted on a printed circuit board, and its lead portions are soldered to a printed pattern of the printed circuit board, flux is prevented from reaching the internal part of the lead portion, and various problems which are otherwise caused by intrusion of flux into the interior of the housing can be effectively prevented.