A box protector for a threaded joint for pipes which is mounted on a box of a threaded joint for pipes having a pin-box structure in order to protect a contact surface of the box, the contact surface of the box having a female threaded portion including complete threads and an unthreaded metal contact portion including at least a shoulder surface, the shoulder surface being sloped so as to recede towards the center axis of the joint by an angle θ with respect to the direction perpendicular to the axis of the threaded joint or being parallel to the perpendicular direction, wherein the box protector has a tubular body made of a resin with an axial length which is longer than that of the contact surface of the box and having a structure which can form a first seal portion and a second seal portion by contacting the box surface on both sides of the contact surface of the box, and wherein the tubular body has on its outer peripheral surface a male threaded portion which threadingly engages with at least a portion of the complete threads of the female threaded portion of the box, wherein: the tubular body of the protector has a shoulder surface which forms a first seal portion which sealingly contacts the shoulder surface of the box, the shoulder surface of the protector slopes to the rear in the direction of insertion of the protector towards the center axis of the joint by an angle θP with respect to the direction perpendicular to the pipe axial direction, and the angle of slope θP of the shoulder surface of the protector is larger than the angle of slope θ of the shoulder surface of the box; the tubular body of the protector has a circumferential groove in its outer peripheral surface in the vicinity of the shoulder surface of the protector, and the position and the cross-sectional shape of the circumferential groove are such that under a torque applied when mounting the protector on the box, a portion of the tubular body in the vicinity of the circumferential groove elastically deforms so as to reduce the distance in the axial direction at the opening of the circumferential groove, thereby ensuring the formation of the first seal portion; the second seal portion is formed by contacting an elastic material attached to the protector with the box surface; and a recess is formed in a rear end surface of the protector, characterized by further comprising a tubular metal body which is open at both ends fitted inside the tubular body, and in that a rear end portion of the tubular metal body is formed with a bent portion which is bent into a circular shape; and in that the tubular metal body is secured to the protector by the spring action of the bent portion which is inserted into the recess. the tubular body of the protector has a shoulder surface which forms a first seal portion which sealingly contacts the shoulder surface of the box, the shoulder surface of the protector slopes to the rear in the direction of insertion of the protector towards the center axis of the joint by an angle θP with respect to the direction perpendicular to the pipe axial direction, and the angle of slope θP of the shoulder surface of the protector is larger than the angle of slope θ of the shoulder surface of the box; the tubular body of the protector has a circumferential groove in its outer peripheral surface in the vicinity of the shoulder surface of the protector, and the position and the cross-sectional shape of the circumferential groove are such that under a torque applied when mounting the protector on the box, a portion of the tubular body in the vicinity of the circumferential groove elastically deforms so as to reduce the distance in the axial direction at the opening of the circumferential groove, thereby ensuring the formation of the first seal portion; the second seal portion is formed by contacting an elastic material attached to the protector with the box surface; and a recess is formed in a rear end surface of the protector, characterized by further comprising a tubular metal body which is open at both ends fitted inside the tubular body, and in that a rear end portion of the tubular metal body is formed with a bent portion which is bent into a circular shape; and in that the tubular metal body is secured to the protector by the spring action of the bent portion which is inserted into the recess.