A semi-automatic scanner for ultrasonic flaw detection comprises a carriage travelling on a guide rail, a guide arm extending in a direction transverse to the travel direction of the carriage and supported by the carriage so as to pivot in a plane transverse to the travel direction of the carriage, a probe holder slidably supported by the arm, and a probe mounted on said probe holder so as to pivot about two axes transverse to each other. One of the axes is generally in parallel to the travel direction of the carriage. The carriage is driven by a motor, and the probe is moved by manual or motor-driving operation in a direction transverse to the travel direction of the carriage while pressing the probe on a surface to be inspected, whereby the probe accurately follows the surface even if the surface is curved.