A Continuous Transmission Frequency Modulated (CTFM) detection apparatus includes a projector, a sensor, and a hardware processor. The projector is configured to transmit underwater a frequency modulated transmission wave based on a transmission signal. The sensor is configured to form a reception beam directed downward and laterally outward to a side of the boat or the ship and receive a reflected wave, the reflected wave comprising a reflection of the transmission wave on a target object. The hardware processor is programmed to at least generate a beat signal based at least in part on the transmission signal and the reflected wave, extract a processing signal from the beat signal, and generate an image information related to the target object based on the extracted processing signal.