A target object detection device is provided. The device includes a transmitter for transmitting at least one transmission wave in a predetermined azimuth, an echo signal receiver for receiving echo signals of the transmission waves, an echo signal suppressor for suppressing levels of the echo signals corresponding to sampling positions, a target object detector for detecting the target object(s) based on the level-suppressed echo signals, a first updater for comparing amplitude level(s) of echo signals of sampling positions, with the threshold that is set in association with the first distance, and determining to update the values with a new threshold and a new suppression value, and a second updater for comparing amplitude level(s) of echo signals of sampling positions, with the threshold that is set in association with the second distance, and determining to update the values with a new threshold and a new suppression value.