A workpiece picking device and method for reducing the cycle time of a picking operation of workpieces, by omitting or reducing the movement of a robot manipulator when an image of the workpieces is captured. An image processor of the picking device includes a camera controlling part for reading image data from a camera, a memory for storing the image data, a workpiece detecting part for extracting one or more images from the memory and detecting one or more workpieces in the image, and a workpiece selecting part for selecting a workpiece to be picked among the workpieces detected by the workpiece detecting part. The image processor further includes a stacked condition judging part for determining whether the condition of the stacked workpieces in a container is changed.