An ultrasonic flaw detecting apparatus for detecting an internal defective state at a bend (Wc) of a laminated part made of composite materials, comprising: an ultrasonic transducer configured to transmit and receive ultrasonic waves; and a controlling unit configured to detect and process the internal defective state at the bend (Wc) of the laminated part according to flaw detecting signals from the ultrasonic transducer, wherein: the ultrasonic transducer includes: a transducer main body that has, on a front end side thereof, an oscillating plane having a bent shape in a side view and corresponding to a larger- or smaller-diameter curved surface formed at the bend (Wc) of the laminated part, and a plurality of oscillators that are distributed over the oscillating plane in a matrix manner in a bent direction of the oscillating plane of the transducer main body and in a perpendicular width direction of the transducer main body, and is configured to transmit ultrasonic waves toward the bend (Wc) of the laminated part and to receive reflected waves from the bend (Wc) of the laminated part; and the controlling unit is configured successively to carry out, for each oscillator group formed of a width-direction row of the plurality of oscillators, switching each of the oscillators in the oscillator group between transmission and reception oscillator modes in turn so that the pattern of transmission and reception oscillators along the width direction changes according to a preset transmission/reception sequence, and processing received signals from the reception oscillators according to an aperture synthesis method. an ultrasonic transducer configured to transmit and receive ultrasonic waves; and a controlling unit configured to detect and process the internal defective state at the bend (Wc) of the laminated part according to flaw detecting signals from the ultrasonic transducer, wherein: the ultrasonic transducer includes: a transducer main body that has, on a front end side thereof, an oscillating plane having a bent shape in a side view and corresponding to a larger- or smaller-diameter curved surface formed at the bend (Wc) of the laminated part, and a plurality of oscillators that are distributed over the oscillating plane in a matrix manner in a bent direction of the oscillating plane of the transducer main body and in a perpendicular width direction of the transducer main body, and is configured to transmit ultrasonic waves toward the bend (Wc) of the laminated part and to receive reflected waves from the bend (Wc) of the laminated part; and a transducer main body that has, on a front end side thereof, an oscillating plane having a bent shape in a side view and corresponding to a larger- or smaller-diameter curved surface formed at the bend (Wc) of the laminated part, and a plurality of oscillators that are distributed over the oscillating plane in a matrix manner in a bent direction of the oscillating plane of the transducer main body and in a perpendicular width direction of the transducer main body, and is configured to transmit ultrasonic waves toward the bend (Wc) of the laminated part and to receive reflected waves from the bend (Wc) of the laminated part; and the controlling unit is configured successively to carry out, for each oscillator group formed of a width-direction row of the plurality of oscillators, switching each of the oscillators in the oscillator group between transmission and reception oscillator modes in turn so that the pattern of transmission and reception oscillators along the width direction changes according to a preset transmission/reception sequence, and processing received signals from the reception oscillators according to an aperture synthesis method.