To provide a liquid flow path switching device which has high switching accuracy, short calibration time, low running cost, and a simple and strong structure.

The liquid flow path switching device comprises a rotating shaft parallel to a flow direction of a jet flow; two commutation blades fixed to the rotating shaft and extended to the flow direction of the jet flow; and a straightening vane which leads a first flow path positioning at one side of the two commutation blades and leads into a second flow path at the other side of the two commutation blades. While the rotation is performed from an initial angle position to a specified angle in one direction, a first commutation blade traverses the jet flow, the flow path is switched from the second flow path to the first flow path; and while the rotation is performed to the specified angle at the same rotation direction, a second commutation blade traverses the jet flow, then the flow path is switched from the first flow path to the second flow path. Accordingly, due to the rotation of the same rotation direction, the initial angle position is kept without traversing the jet flow again, the rotation operation to continue in the same rotation direction is made possible.