Ultrasonic inspection device and ultrasonic inspection unit

An ultrasonic inspection device inspecting an object to be inspected including molten metal, comprising:

• a longitudinal ultrasonic sensor configured to emit and receive a longitudinal ultrasonic wave;
• and
• an ultrasonic transducer unit made of metal and having a shape of a polyhedron, the ultrasonic transducer unit including
• an output surface configured to be disposed facing the object to be inspected,
• an input surface on which the longitudinal ultrasonic sensor is disposed, and
• a conversion surface configured to, when the longitudinal ultrasonic wave input through the input surface is reflected by the conversion surface, convert the longitudinal ultrasonic wave into a transverse ultrasonic wave such that the transverse ultrasonic wave propagates toward the output surface, the conversion surface being tilted at a predetermined angle with respect to an in-plane direction of the output surface, wherein
• a thermal conductivity of the ultrasonic transducer unit is lower than thermal conductivity of the object to be inspected, and the thermal conductivity of the ultrasonic transducer unit is 100 W/m· K or less.