A rotor type open-end spinning frame spins a yarn from a fiber bundle formed from unraveled fibers at a fiber collecting section while applying a twist to the fiber bundle during normal spinning, and which pieces the fiber bundle to a standard thread supplied to the fiber collecting section during yarn piecing. The spinning frame has a rotatable outer rotor which has an inner wall with a fiber collecting section. A conduit member is fixed opposite the open-end of the outer rotor and induct the fiber bundle and the standard thread therethrough. An inner rotor is disposed coaxially to and rotatable in the outer rotor. The inner rotor rotates independently of the outer rotor during both normal spinning and yarn piecing. A passage in the inner rotor communicates with the conduit member and guides the fiber bundle from the fiber collecting section to the conduit member during yarn spinning. Another passage in the inner rotor communicates with the conduit member and introduces the standard thread into the fiber collecting section from the conduit member during yarn piecing. A restriction device in the inner rotor retains the fiber bundle within the first passage by engaging with the fiber bundle during yarn spinning.