We investigated emergence of a twisted flux tube into a solar corona by performing a three-dimensional MHD simulation. After emerging, outer field lines composing the envelope of the flux tube expanded to form a potential field-like (shearless) arcade, while inner field lines underlying an axis of the flux tube formed sigmoidal structure. The underlying inner field lines had footpoints in a chromospheric layer where high current density was distributed, suggesting that a plasma distributed along these inner field lines could be heated via dissipation of the intense current at their chromospheric footpoints associated with efficient thermal conduction along the field lines, observed as a soft X-ray sigmoid (Magara & Longcope 2001).