A paper medium skew correcting device includes: a support including a pair of fixed stop plates arranged in parallel; a skew correcting tapered roller assembly including a tapered roller, a reference plate located at a large end face of the tapered roller and a transmission shaft; a tapered cover plate covering on the tapered roller with a skew correcting passage formed between an inner wall of the tapered cover plate and an outer wall of the tapered roller, an auxiliary pressure roller mechanism is mounted on an outer wall of the tapered cover plate and is configured to press a paper medium against the outer wall of the tapered roller tightly, the tapered cover plate is provided with an opening; and a driving transmission assembly. The device fully uses combined action of centrifugal force and friction force to realize skew correction and conveying of the paper medium.