1. An ultrasonic flaw detector comprising: a first flaw detection head including a first probe; a second flaw detection head including a second probe; a moving mechanism that causes the first flaw detection head and the second flaw detection head to perform scanning; a first calibration area in which a first calibration standard sample is disposed; a second calibration area in which a second calibration standard sample is disposed; a flaw detection area in which an inspection object is disposed; and a controller that is configured to perform a second calibration process of causing the second flaw detection head to scan the second calibration standard sample to perform calibration using the second calibration standard sample either in a case where the controller performs a first calibration process of causing the first flaw detection head to scan the first calibration standard sample to perform calibration using the first calibration standard sample or in a case where the controller performs a first flaw detection process of performing ultrasonic flaw detection inspection of the inspection object by the first flaw detection head; wherein the flaw detection area is interposed between the first calibration area and the second calibration area.