A friction stir spot welding apparatus including a rotary tool configured to move forward and backward along a rotational axis, the friction stir spot welding apparatus being suitable for pressing a distal end of the rotary tool on workpieces (60, 61, 62), the workpieces (60, 61, 62) being a first member and a second member, which are laid one on top of the other and between which a sealant is applied to a contacting portion of the first member and a contacting portion of the second member, the contacting portions contacting each other; and for rotating a contacting part of the rotary tool, the contacting part contacting the workpieces (60, 61, 62), such that the workpieces (60, 61, 62) are softened by frictional heat and stirred to be joined together, the friction stir spot welding apparatus comprising: a columnar pin member; a cylindrical shoulder member, in which the pin member is inserted; a rotation driver configured to rotate the pin member and the shoulder member about an axis that coincides with a central axis of the pin member; a cylindrical clamp member, in which the pin member and the shoulder member are inserted; a forward/backward movement driver configured to move each of the pin member, the shoulder member, and the clamp member forward and backward along the axis; and a controller, wherein the friction stir spot welding apparatus is characterized in that the controller is configured to perform a preliminary operation of controlling the forward/backward movement driver, such that at least one of the pin member and the shoulder member presses the workpieces (60, 61, 62) before the clamp member presses the workpieces (60, 61, 62); and then to perform a joining operation of controlling the rotation driver and the forward/backward movement driver, such that the pin member and the shoulder member stir the workpieces (60, 61, 62). a columnar pin member; a cylindrical shoulder member, in which the pin member is inserted; a rotation driver configured to rotate the pin member and the shoulder member about an axis that coincides with a central axis of the pin member; a cylindrical clamp member, in which the pin member and the shoulder member are inserted; a forward/backward movement driver configured to move each of the pin member, the shoulder member, and the clamp member forward and backward along the axis; and a controller, wherein the friction stir spot welding apparatus is characterized in that the controller is configured to perform a preliminary operation of controlling the forward/backward movement driver, such that at least one of the pin member and the shoulder member presses the workpieces (60, 61, 62) before the clamp member presses the workpieces (60, 61, 62); and then to perform a joining operation of controlling the rotation driver and the forward/backward movement driver, such that the pin member and the shoulder member stir the workpieces (60, 61, 62). perform a preliminary operation of controlling the forward/backward movement driver, such that at least one of the pin member and the shoulder member presses the workpieces (60, 61, 62) before the clamp member presses the workpieces (60, 61, 62); and then to perform a joining operation of controlling the rotation driver and the forward/backward movement driver, such that the pin member and the shoulder member stir the workpieces (60, 61, 62).