A connector structure comprising: an outer housing including a housing main unit with a tubular shape and an arm that protrudes from a first wall portion of the housing main unit to a space portion surrounded by the housing main unit; an inner housing disposed interior to the housing main unit, the inner housing holding a first terminal; and a detection member supported between the first wall portion and the inner housing slidably along an axial direction of the housing main unit, wherein the housing main unit has an opening portion in which a counterpart housing is inserted in an insertion direction, the counterpart housing including a protrusion and holding a second terminal, the arm includes an arm main unit with flexibility that extends toward the opening portion and a lock tab that protrudes from the arm main unit, when the counterpart housing is inserted in the housing main unit through the opening portion, the arm main unit of the arm is elastically deformed to enable the lock tab to ride over and lock the protrusion, and when the counterpart housing is inserted into the housing main unit, the lock tab locks the detection member to restrict motion of the detection member toward the opening portion while the lock tab has not yet ridden over the protrusion, and the lock tab allows the detection member to move toward the opening portion after the lock tab completes riding over the protrusion, characterized in that the arm main unit includes a pair of first arm portions, a beam portion, a pair second arm portions and an operating portion, the pair of first arm portions protrudes from the first wall portion, extends toward the opening portion, and are disposed in juxtaposition with, and to be spaced away from, each other along a width direction orthogonal to the insertion direction, the beam portion joins a distal ends of the pair of first arm portions, the pair of second arm portions extends from the beam portion toward a side opposite to the opening portion with the pair of first arm portions interposed therebetween, and the operating portion joins a distal ends of the pair of second arm portions and exposed to the outside of the housing main unit. an outer housing including a housing main unit with a tubular shape and an arm that protrudes from a first wall portion of the housing main unit to a space portion surrounded by the housing main unit; an inner housing disposed interior to the housing main unit, the inner housing holding a first terminal; and a detection member supported between the first wall portion and the inner housing slidably along an axial direction of the housing main unit, wherein the housing main unit has an opening portion in which a counterpart housing is inserted in an insertion direction, the counterpart housing including a protrusion and holding a second terminal, the arm includes an arm main unit with flexibility that extends toward the opening portion and a lock tab that protrudes from the arm main unit, when the counterpart housing is inserted in the housing main unit through the opening portion, the arm main unit of the arm is elastically deformed to enable the lock tab to ride over and lock the protrusion, and when the counterpart housing is inserted into the housing main unit, the lock tab locks the detection member to restrict motion of the detection member toward the opening portion while the lock tab has not yet ridden over the protrusion, and the lock tab allows the detection member to move toward the opening portion after the lock tab completes riding over the protrusion, characterized in that the arm main unit includes a pair of first arm portions, a beam portion, a pair second arm portions and an operating portion, the pair of first arm portions protrudes from the first wall portion, extends toward the opening portion, and are disposed in juxtaposition with, and to be spaced away from, each other along a width direction orthogonal to the insertion direction, the beam portion joins a distal ends of the pair of first arm portions, the pair of second arm portions extends from the beam portion toward a side opposite to the opening portion with the pair of first arm portions interposed therebetween, and the operating portion joins a distal ends of the pair of second arm portions and exposed to the outside of the housing main unit.