Abstract: A watertight connector is provided with an inertial locking mechanism, housings of which can be connected while making an operator feel and notice the completion of a connecting operation. The inertial locking mechanism 17 has resistance arms 22 and contact ribs 15 and is provided between male and female housings 11 and 20. A front annular projection 28A of a waterproof ring 27 mounted on the female housing 11 is brought into contact with the leading end of a receptacle 12 of a male housing 20 at a timing when the resistance arms 22 and the contact ribs 15 are brought into contact with each other during a connecting operation of the housings 11, 20. Thus, a peak P3 of a connection resistance value of the waterproof ring 27 and a peak P4 of a connection resistance value of the inertial locking mechanism 17 are synchronized to generate a large connection resistance, and a large inertial force can be obtained when this large connection resistance disappears.