A portable ultrasonic testing device which with respect to a plate material having a chamfered surface formed between an outer plate surface and an inner peripheral surface, irradiates the chamfered surface with ultrasonic waves while moving along the chambered surface to thereby detect flaws in the plate material is provided with: a device frame; a probe which irradiates the chambered surface with the ultrasonic waves, and receives reflected ultrasonic waves; a wedge to which the probe is fixed and which is able to come into contact with the chamfered surface; a slide mechanism which moves the wedge in a sliding direction with respect to the device frame; a spring member which is urged in a direction in which the wedge and the chamfered surface approach each other in the sliding direction; and a movable roller and a pair of fixed rollers which are provided in the device frame and each have a rolling contract surface that is in contact with the inner peripheral surface.