A contact member for a gas sensor in which an electric connection to a sensor element is obtained by pinching and fixing said sensor element in an insertion port formed by a pair of housing members, comprising: said pair of housing members opposed to each other and forming said insertion port; a constraint member (25, 125, 225, 325) which is provided in an outer periphery of said pair of housing members and has a constraining function of constraining a displacement of said pair of housing members within a predetermined range; and an annular member which is provided in an outer periphery of said constraint member and is adapted and arranged to undergo contractive deformation when receiving an external force in a state that said sensor element is inserted in said insertion port, in such a way that said pair of housing members and said sensor element are brought into pressure contact, and said sensor element is pinched and fixed by said pair of housing members in a state that an electrode terminal provided in said sensor element comes into contact with a contact point member provided in said pair of housing members; said contact member being characterized in that: said constraint member (25, 125, 225, 325) is constructed by a first member (25a, 125a, 225a, 325a) and a second member (25b, 125b, 225b, 325b); said constraint member (25, 125, 225, 325) is provided with two sets of engaging mechanisms (254, 255; 2255, 2256; 3255, 3256) which engage said first member and said second member; each of said two sets of engaging mechanisms is constructed by an engaging part (254, 2255, 3255) which is provided in one of said first member (25a, 125a, 225a, 325a) and said second member (25b, 125b, 225b, 325b) and an engaged part (255, 2256, 3256) which is provided in the other, in such a way that: the engagement of said first member and said second member causes constraint of displacement of said pair of housing members within a predetermined range before said sensor element is pinched and fixed by said pair of housing members, and the engagement of said two sets of engaging mechanisms is released when the constraint member is pinched between the annular member and the pair of housing members. said pair of housing members opposed to each other and forming said insertion port; a constraint member (25, 125, 225, 325) which is provided in an outer periphery of said pair of housing members and has a constraining function of constraining a displacement of said pair of housing members within a predetermined range; and an annular member which is provided in an outer periphery of said constraint member and is adapted and arranged to undergo contractive deformation when receiving an external force in a state that said sensor element is inserted in said insertion port, in such a way that said pair of housing members and said sensor element are brought into pressure contact, and said sensor element is pinched and fixed by said pair of housing members in a state that an electrode terminal provided in said sensor element comes into contact with a contact point member provided in said pair of housing members; said contact member being characterized in that: said constraint member (25, 125, 225, 325) is constructed by a first member (25a, 125a, 225a, 325a) and a second member (25b, 125b, 225b, 325b); said constraint member (25, 125, 225, 325) is provided with two sets of engaging mechanisms (254, 255; 2255, 2256; 3255, 3256) which engage said first member and said second member; said constraint member (25, 125, 225, 325) is constructed by a first member (25a, 125a, 225a, 325a) and a second member (25b, 125b, 225b, 325b); said constraint member (25, 125, 225, 325) is provided with two sets of engaging mechanisms (254, 255; 2255, 2256; 3255, 3256) which engage said first member and said second member; each of said two sets of engaging mechanisms is constructed by an engaging part (254, 2255, 3255) which is provided in one of said first member (25a, 125a, 225a, 325a) and said second member (25b, 125b, 225b, 325b) and an engaged part (255, 2256, 3256) which is provided in the other, in such a way that: the engagement of said first member and said second member causes constraint of displacement of said pair of housing members within a predetermined range before said sensor element is pinched and fixed by said pair of housing members, and the engagement of said two sets of engaging mechanisms is released when the constraint member is pinched between the annular member and the pair of housing members. the engagement of said first member and said second member causes constraint of displacement of said pair of housing members within a predetermined range before said sensor element is pinched and fixed by said pair of housing members, and the engagement of said two sets of engaging mechanisms is released when the constraint member is pinched between the annular member and the pair of housing members.