A workpiece detector includes a camera to acquire a two-dimensional image of a search range within which workpieces are disposed. A three-dimensional sensor detects a three-dimensional shape of a three-dimensional detection area. A workpiece extraction section processes the two-dimensional image to extract candidate workpieces. An area setting section sets a three-dimensional detection areas respectively corresponding to the candidate workpieces. A prioritizing section sets an order of priority to the three-dimensional detection areas to give higher priority to one three-dimensional detection area containing more of the candidate workpieces. A sensor control section controls the three-dimensional sensor to detect the three-dimensional shape of each three-dimensional detection area in the order of priority. Every time the three-dimensional shape is detected, a workpiece detection section searches the workpieces based on the detected three-dimensional shape to detect a pickable workpiece.