A connector is provided with a housing 10 fittable into a receptacle 52 of a mating connector 50 and a retainer 20 to be inserted into the housing 10 sideways. Cavities 12A, 12B for accommodating terminals are arranged side by side in the housing. The retainer 20 includes a main body 21 with side by side engaging portions 26A, 26B for engaging the terminals. Side walls 31 are provided at the opposite ends in an arrangement direction of the engaging portions 26A, 26B and projecting forward from the main body 21 in a connecting direction with the mating connector 50. Reinforcements 34 project in from front end portions of the side walls 31 in the connecting direction with the mating connector 50 and are at the rear ends of the side walls 31 in an inserting direction of the retainer 20 into the housing 10.