A waterproof rubber plug has a through hole through which an electric wire is inserted to be connected to a terminal. A connector housing includes a terminal chamber for accommodating the terminal and a wall portion having a through hole formed so as to oppose to the terminal chamber, through which the electric wire is inserted. A recess for accommodating the rubber plug to thereby seal the electric wire and the terminal chamber. The recess is formed on an inner side face of the wall portion of the connector housing so as to communicate with the through hole of the wall portion. A window hole is formed on a part of the wall portion surrounding the recess so as to expose an anti-sealing part of the rubber plug accommodated in the recess.