A gear grinding machine for use in grinding a gear to be machined while rotating a grinding wheel and the gear in mesh with each other, the gear grinding machine comprising: a dresser which is configured to be rotationally driven to dress the grinding wheel; and dresser pivoting means for pivoting the dresser between a dressing position where the dresser can dress the grinding wheel and a retreat position where the dresser retreats from the dressing position at the time of grinding, about a pivot parallel to a work rotation axis of the gear and perpendicular to a feed direction of the grinding wheel to the gear, wherein the dresser pivoting means comprises: a rotating portion by which the dresser is rotatably supported and which is configured to rotate about the pivot; a fixing portion by which the rotating portion is rotatably supported; positioning means for positioning rotation of the rotating portion with respect to the fixing portion; positioning release means; and rotation means for allowing the rotating portion to rotate when the positioning release means actuates; characterized in that the positioning release means is provided in the fixing portion, is configured to use leverage to release the positioning by the positioning means, and comprises: a cylinder portion formed in the fixing portion; a piston member housed in the cylinder portion to be slidable in the direction of the pivot; an annular groove portion formed in the rotating portion; a lever having a base end portion swingably supported by the fixing portion and a tip portion held by the piston member; rollers fitted into the groove portion and rotatably supported by the lever; and pressure feeding and discharging means for feeding and discharging pressure to/from the cylinder portion to allow the piston member to slide. a dresser which is configured to be rotationally driven to dress the grinding wheel; and dresser pivoting means for pivoting the dresser between a dressing position where the dresser can dress the grinding wheel and a retreat position where the dresser retreats from the dressing position at the time of grinding, about a pivot parallel to a work rotation axis of the gear and perpendicular to a feed direction of the grinding wheel to the gear, wherein the dresser pivoting means comprises: a rotating portion by which the dresser is rotatably supported and which is configured to rotate about the pivot; a fixing portion by which the rotating portion is rotatably supported; positioning means for positioning rotation of the rotating portion with respect to the fixing portion; positioning release means; and rotation means for allowing the rotating portion to rotate when the positioning release means actuates; a rotating portion by which the dresser is rotatably supported and which is configured to rotate about the pivot; a fixing portion by which the rotating portion is rotatably supported; positioning means for positioning rotation of the rotating portion with respect to the fixing portion; positioning release means; and rotation means for allowing the rotating portion to rotate when the positioning release means actuates; characterized in that the positioning release means is provided in the fixing portion, is configured to use leverage to release the positioning by the positioning means, and comprises: a cylinder portion formed in the fixing portion; a piston member housed in the cylinder portion to be slidable in the direction of the pivot; an annular groove portion formed in the rotating portion; a lever having a base end portion swingably supported by the fixing portion and a tip portion held by the piston member; rollers fitted into the groove portion and rotatably supported by the lever; and pressure feeding and discharging means for feeding and discharging pressure to/from the cylinder portion to allow the piston member to slide. a cylinder portion formed in the fixing portion; a piston member housed in the cylinder portion to be slidable in the direction of the pivot; an annular groove portion formed in the rotating portion; a lever having a base end portion swingably supported by the fixing portion and a tip portion held by the piston member; rollers fitted into the groove portion and rotatably supported by the lever; and pressure feeding and discharging means for feeding and discharging pressure to/from the cylinder portion to allow the piston member to slide.