An internal gear grinding machine achieves space savings and reduction in size of a machine, as well as prevents the tools from being damaged even when an abnormal situation such as a blackout occurs, by a simplifying dressing operation. The internal gear grinding machine for grinding a workpiece (W) by synchronously rotating the workpiece (W) and a barrel-shaped threaded grinding wheel (17) in mesh with each other includes a dressing device (20) for dressing the threaded tool (17) by meshing the threaded grinding wheel (17) with a disk dresser (56). When dressing, the threaded grinding wheel (17) and the disc dresser (56) are operated in accordance with the helix angle and barrel shape of the threaded grinding wheel (17), and the brake mechanism (58) applies a braking force to a dresser turn drive motor (53) to enable the disc dresser (56) to be maintained at a turned position thereof.