Abstract: A length measuring apparatus employing a magnetostrictive delay line according to the present invention includes a drive coil (4), a receiving coil (3) provided on an outer periphery of the magnetostrictive delay line (1) over the whole length measuring range thereof, the magnetostrictive delay line (1) uniformly magnetized in its length direction, and a short-circuit ring (2) disposed over an outer periphery of the receiving coil (3). Ultrasonic vibration (C) is generated in the magnetostrictive delay line (1) by using the drive pulse (A) applied to the drive coil (4). A pulse current (B) generated in the receiving coil (3) is detected when the ultrasonic vibration (C) is propagated in the magnetostrictive delay line (1) and passes by a position where the short-circuit ring (2) is disposed. A position of the short-circuit ring (2) is measured based on a time from generation of the drive pulse (A) to generation of the pulse current (B) in the detection coil 3.