A machine tool is known which machines a workpiece attached to a spindle by using a tool disposed on a tool rest which can relatively move with respect to the spindle or a table. Among such machine tools, there is known a machine tool including a workpiece supply/conveyance device which automatically convey a machined workpiece from the spindle and automatically supplies an unmachined workpiece to the spindle.
A workpiece supply/conveyance device of a machine tool disclosed in Patent Document 1 includes a plurality of arms radially expanding from a common rotation center. Each arm is integrally rotated around the rotation center as a supporting point, and a position of each arm is sequentially switched to a machined workpiece conveying position, a workpiece supply position, a standby position, and a workpiece delivery/reception position facing the spindle, whereby an unmachined workpiece is prepared and delivered to the spindle, and a machined workpiece is received from the spindle and then conveyed.
Further, a loading device disclosed in Patent Document 2 includes four arms which rotate in forward and reverse directions simultaneously performs an operation of delivering an unmachined workpiece from an arm A to one of two spindles arranged in parallel when the four arms are placed at predetermined positions, an operation of delivering a half-machined workpiece to the other spindle from an arm B, and an operation of delivering the half-machined workpiece to an arm C, and then simultaneously carries out the loading of the unmachined workpiece to the arm A and the unloading of a machined workpiece from an arm D, when the four arms are integrally rotated to be placed at next predetermined positions.
However, in the workpiece supply/conveyance device disclosed in each of Documents 1 and 2, the workpiece loading arm which delivers the unmachined workpiece to the spindle and the workpiece unloading arm which receives the machined workpiece from the spindle are separately disposed. Therefore, after the workpiece unloading arm has received the machined workpiece from the spindle, until the workpiece loading arm which holds an unmachined workpiece rotates to a position where it faces the spindle, a long time is required, and hence there is a problem that a cycle time is prolonged.    Patent Document 1: Japanese Patent Application Laid-open No. 155196-1983    Patent Document 2: Japanese Patent Application Laid-open No. 75901-1986
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