A connector, comprising: a housing main body to be connected to a mating housing; a lock arm projecting from the housing main body, and being resiliently deformable in a deforming direction, wherein a lock projection of the lock arm is at least partly resiliently fittable into a lock receiving portion of the mating housing from below or inside to hold the housing main body and the mating housing in a connected state; and a detecting member to be mounted on or to the housing main body movably from an initial position to a detection position, including a resilient arm portion resiliently deformable in the deforming direction; wherein an accommodating recess is formed on a lower surface of the lock arm, which is open on a surface facing toward a deformation space and/or on a rear surface of the lock projection, and wherein the accommodating recess is so dimensioned and/or shaped that a protrusion of the detecting member is at least partly fittable thereinto, wherein a contact portion is formed to project forward on a lower end part of the front end of the protrusion of the detecting member, wherein, when the detecting member is at the initial position, an upper or outer surface of the contact portion comes into contact with an inner upper surface of the accommodating recess from below, so that the resilient arm portion is resiliently deformed with a pre-load applied to the lock arm, wherein an insertion movement of the detecting member is restricted at the initial position by the contact of the resilient arm portion with the lock arm before the housing main body is connected to the mating housing, and wherein a movement restricted state at the initial position is released and the detecting member is capable of reaching the detection position where the resilient arm portion at least partly enters the deformation space by being displaced from the initial position when the housing main body is properly connected to the mating housing. a housing main body to be connected to a mating housing; a lock arm projecting from the housing main body, and being resiliently deformable in a deforming direction, wherein a lock projection of the lock arm is at least partly resiliently fittable into a lock receiving portion of the mating housing from below or inside to hold the housing main body and the mating housing in a connected state; and a detecting member to be mounted on or to the housing main body movably from an initial position to a detection position, including a resilient arm portion resiliently deformable in the deforming direction; wherein an accommodating recess is formed on a lower surface of the lock arm, which is open on a surface facing toward a deformation space and/or on a rear surface of the lock projection, and wherein the accommodating recess is so dimensioned and/or shaped that a protrusion of the detecting member is at least partly fittable thereinto, wherein a contact portion is formed to project forward on a lower end part of the front end of the protrusion of the detecting member, wherein, when the detecting member is at the initial position, an upper or outer surface of the contact portion comes into contact with an inner upper surface of the accommodating recess from below, so that the resilient arm portion is resiliently deformed with a pre-load applied to the lock arm, wherein an insertion movement of the detecting member is restricted at the initial position by the contact of the resilient arm portion with the lock arm before the housing main body is connected to the mating housing, and wherein a movement restricted state at the initial position is released and the detecting member is capable of reaching the detection position where the resilient arm portion at least partly enters the deformation space by being displaced from the initial position when the housing main body is properly connected to the mating housing.