A valve core comprising: a first core cylinder body having a male screw (22N, 23N) to be screwed into a female screw of a core mounting hole; a second core cylinder body arranged on a deeper side than the first core cylinder body in the core mounting hole and having an opening as a valve opening on an opposite side to the first core cylinder body; an outer peripheral seal portion provided on the second core cylinder body and to be in close contact with a portion on a deeper side than the female screw of the core mounting hole; a movable member having a valve body to open and close the valve opening at an end of a shaft section linearly movably penetrating inside the first core cylinder body and the second core cylinder body; an elastic member in contact with the movable member and the first core cylinder body and biasing so as to sandwich the second core cylinder body between the first core cylinder body and the valve body; and a pair of fitting sections (21, 26) including a first fitting section (21, 26) and a second fitting section (21, 26) which are provided in the first core cylinder body and the second core cylinder body and which are rotatably fitted to each other and are separable without interfering with each other, wherein the pair of fitting sections (21, 26) have cylindrical shapes that are detachably fitted to each other, and the first fitting section (21, 26) has a stepped surface (21B, 26B) with which an end surface (21A, 26A) of the second fitting section (21, 26) is in contact, characterized in that a fitting depth of the pair of fitting sections (21, 26) is larger than a linear movement stroke of the movable member when the movable member cannot be pushed down any further. a first core cylinder body having a male screw (22N, 23N) to be screwed into a female screw of a core mounting hole; a second core cylinder body arranged on a deeper side than the first core cylinder body in the core mounting hole and having an opening as a valve opening on an opposite side to the first core cylinder body; an outer peripheral seal portion provided on the second core cylinder body and to be in close contact with a portion on a deeper side than the female screw of the core mounting hole; a movable member having a valve body to open and close the valve opening at an end of a shaft section linearly movably penetrating inside the first core cylinder body and the second core cylinder body; an elastic member in contact with the movable member and the first core cylinder body and biasing so as to sandwich the second core cylinder body between the first core cylinder body and the valve body; and a pair of fitting sections (21, 26) including a first fitting section (21, 26) and a second fitting section (21, 26) which are provided in the first core cylinder body and the second core cylinder body and which are rotatably fitted to each other and are separable without interfering with each other, wherein the pair of fitting sections (21, 26) have cylindrical shapes that are detachably fitted to each other, and the first fitting section (21, 26) has a stepped surface (21B, 26B) with which an end surface (21A, 26A) of the second fitting section (21, 26) is in contact, characterized in that a fitting depth of the pair of fitting sections (21, 26) is larger than a linear movement stroke of the movable member when the movable member cannot be pushed down any further.