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