The present invention provides a signal processing device for optical discs that is capable of more accurately check signal quality at a higher speed than the conventional technique, even if a playback RF signal is deteriorated. A short recording mark detecting unit 115 detects short recording marks in an RF signal read from an optical disc 101, the short recording mark counting unit 116 counts a first short recording mark number as the number of the detected short recording marks, an error number counting unit 110 counts errors in the RF signal, an error number converting unit 111 converts the number of the errors to a second short recording mark number equivalent to the number of the errors, and a signal quality judging unit 112 judges recording quality based on a total of the first and second short recording mark numbers.