Technical field [0001] The present disclosure relates to a threaded joint, and more particularly to a threaded joint for connecting steel pipes. BACKGROUND [0002] Conventionally, oil wells and natural gas wells and the like (hereinafter, collectively referred to as oil well), the steel pipe called oil well pipe is used. OCTG are installed in oil wells are connected to each other by a screw joint. [0003] 　Format of the threaded joint is roughly classified into a integral type coupling type. The integral-type, oil well pipes to each other are directly connected. More specifically, the female screw portion provided on the inner periphery of the tube end portion of one oil well pipe, by male screw portion provided on the outer periphery of the tube end of another oil well pipe is screwed, the oil well pipes to each other It is connected. The coupling type, oil well pipes to each other are connected through the coupling of the tubular. Specifically, each of the female screw portion provided on the inner periphery of the two pipe ends of the coupling, by a male screw portion provided on the outer periphery of the pipe end portion of the oil well pipe is screwed, connecting the oil country tubular goods to each other It is. [0004] 　Generally, the tube end of the oil well pipe male thread portion is formed is referred to as pin from the containing elements to be inserted into the female screw portion. Tube end of the tube end portion or coupling oil well pipes internally threaded portion is formed is referred to as boxes because it contains elements for receiving the external thread portion. [0005] 　In recent years, with the deep well of the oil well, multi-string design to bury the oil country tubular goods to multi-layer has been employed in many cases. The multi-stage string design, it is preferable that the clearance between the outer oil well pipe and an inner OCTG minimized. Therefore, integral type of threaded joint is used. This threaded joint is, for example, about 110% of the outside diameter outside diameter of the pin of the box, generally, a semi-flash type and flash type, etc. (hereinafter, referred to as a semi-flash type are collectively) called. [0006] 　In Japanese Patent No. 3808562 publication, threaded joints intended for use in deep wells have been proposed. The inner end and an outer end portion of the tube axis direction of the threaded joint, the sealing portion and the outer sealing portion are provided respectively. Threaded portion is configured as a whole two-stage tapered thread, having lost screws at each end of the inner seal portion side and the outer seal portion. The disappearance screw of the inner seal portion side, thread crest surface of the female screw portion of the screw trough bottom and the box of the external thread portion of the pin is formed so as to be parallel to the tube axis a constant diameter. The disappearance screw of the outer seal portion side, thread root bottom surface of the female screw portion of the screw crest surface and the box of the external thread portion of the pin is formed so as to be parallel to the tube axis a constant diameter. SUMMARY OF THE DISCLOSURE [0007] 　The threaded joint, typically, high sealing performance is required. If semi-flash type threaded joint, under strict dimensional constraints, it is necessary to ensure a high sealing performance. However, if the threaded joint Japanese Patent No. 3808562, the sealing performance by the disappearance screws mentioned above might decrease. [0008] 　The present disclosure aims to provide a threaded joint capable of ensuring high sealing performance. [0009] 　A threaded joint according to the present disclosure, connects the steel pipes. Threaded joint comprises a pin and a box. Pin constitutes the tube end of one steel pipe. Box constitutes the tube end of another steel pipe. Box, the pin is fastened to the inserted into the pin. Pin includes a inner pin sealing surface, and the pin outer sealing surface, and an inner male screw portion, and the outer male thread portion, and a Pinshoruda surface. Pin the sealing surface is formed on the outer periphery of the distal end portion of the pin. Pin outside sealing surface is formed on an outer peripheral end of the tube main body side of one steel pipe at pin. Internal male screw portion is disposed between the pin in the seal surface and the pin outer sealing surface. Internal male screw portion is formed on the outer circumference of the pin. Outer male thread portion is disposed on the pin outside the seal surface than the inner male screw portion between the pin within the sealing surface and the pin outer sealing surface. Outer male thread portion is formed on the outer circumference of the pin. Pinshoruda surface is disposed between the inner male screw portion and the outer male thread portion. Pinshoruda surface is formed on the outer circumference of the pin. Box comprises a box sealing surface, and the box outside sealing surface, and an inner female thread portion, and the outer internally threaded section, and a box shoulder surface. Box sealing surface, corresponding to the pin sealing surface is formed on the inner periphery of the box. Box sealing surface contacts the pin within the sealing surface in the engaged state. Out of box sealing surface, corresponding to the pin outside the sealing surface is formed on the inner periphery of the box. Out of box sealing surface contacts the pin out of the sealing surface in the engaged state. Internal female threaded portion, corresponding to the inner male screw portion is formed on the inner periphery of the box. Inner female thread portion mate with the inner male screw portion in the engaged state. External female screw portion is formed on the inner periphery of the box corresponding to the outer male thread portion. External female thread portions, mate with external male screw portion in the engaged state. Box shoulder surface is formed on the inner periphery of the box in response to Pinshoruda surface. Box shoulder surface contacts the Pinshoruda surface in engagement state. Internal male screw portion includes a first parallel portion. The first parallel portion is located at the end of the pin within the sealing surface of the inner male screw portion. The first parallel portion, in the longitudinal cross section of the pin includes a plurality of thread root bottom surface formed parallel to the tube axis of one steel pipe. Internal female threaded portion includes a first tapered portion. The first tapered portion, opposed to the first parallel portion in the engaged state. The first taper portion has a first Sato thread height greater than the thread height of the parallel portion, and a thread diameter becomes smaller toward the box sealing surface. Pin the sealing surface has a maximum diameter greater than the minimum diameter of the thread crest surface of the first tapered portion. In longitudinal section of the pin and box of the non-engaged state, the difference in the difference in the diameter of the screw crest surfaces adjacent the first tapered portion Da, and the maximum diameter of the diameter and the pin within the sealing surface of the thread root bottom surface of the first parallel part the when the Db, Da satisfy