Abstract: The present invention relates to a flaw detector imaging apparatus for detecting and visualizing a flaw in a target material to be investigated, comprising an ultrasonic phase-array probe comprising an array of ultrasonic transducers and a flaw detector. The flaw detector includes at least one trigger channel to trigger ultrasonic emitting transducers of the array at respective time delays to produce an ultrasonic beam propagating through the target material, and at least one receiver channel to receive echo signals produced by ultrasonic receiving transducers of the array in response to ultrasonic wave echoes reflected from a flaw in the target material. The receiver channel comprises a delay circuit imparting to the received echo signals the respective time delays as used in the triggering of the ultrasonic emitting transducers and a combiner of the delayed echo signals.