The present invention relates to an ultrasonic inspection device for small bore pipes comprising: a first arc-shaped frame part and a second arc-shaped frame part which surround the circumference of a pipe when combined with the pipe, and which have one side thereof rotationally connected to each other by means of a rotary connecting pin; an adjustment part that connects the other side of the first arc-shaped frame part and the other side of the second arc-shaped frame part to each other and is capable of adjusting the diameter of the bore formed by the first arc-shaped frame part and the second arc-shaped frame part according to the diameter of the pipe; a probe fixing part for fixing a probe to the first arc-shaped frame part such that the probe comes into contact with the surface of the pipe; an encoder part which is provided to the second arc-shaped frame part and maintains an encoder at a predetermined distance from the pipe; and a plurality of roller parts which are provided to the first arc-shaped frame part and the second arc-shaped frame part and rotate around the circumference of the pipe contacting the pipe in a state where the first arc-shaped frame part and the second arc-shaped frame part are connected to each other. The present invention includes two arc-shaped frame parts which surround the circumference of a pipe and is able to adjust the diameter of the bore of a ring-shaped frame part obtained according to connection of the two arc-shaped frame parts, and thus is applicable irrespective of the diameter of the pipe within a predetermined range, thereby improving work convenience and reducing costs.