The present invention discloses a differential signal skew detecting circuit configured to detect a skew of a differential signal. An embodiment of the circuit includes: a common mode voltage outputting circuit configured to output a common mode reference voltage and a common mode skew voltage; and a skew detecting circuit configured to inspect the common mode reference voltage and the common mode skew voltage according to a clock signal so as to output a skew detection value, in which when the skew detecting circuit detects the skew of the differential signal, the skew detection value is a first value, and when the skew detecting circuit detects no skew of the differential signal, the skew detection value is a second value.