To provide a machine tool not only capable of machining an inner surface of a workpiece into a spherical surface but also capable of machining a bearing surface including a flat surface and machining the combination of a spherical surface and a flat surface, and to provide a workpiece inner surface machining method using the machine tool. A machine tool includes: a workpiece holding mechanism 3 holding the workpiece 21; a tool 20 having a supporting member 22 and a cutting tool 23 which is supported to be pivotable about a pivot axis b located on a plane perpendicular to an axis a of the supporting member 22 and has a cutting edge 23a at least at one end; an axial feed mechanism 6a rotating the supporting member 22 about the axis a and moving the supporting member 22 in a direction of the axis a; a pivot driving mechanism 31 pivoting the cutting tool 23 about the pivot axis b; and a machining control mechanism controlling a pivot angle θ of the cutting tool 23 decided by the pivot driving mechanism 31 and a rotation speed and a position in the axis a direction of the supporting member 22 decided by the axial feed mechanism 6a, so as to make a machining point P by the cutting edge 23a move along a desired machining line.