To provide a urinal flushing device capable of preventing a human body from being erroneously detected due to the oscillation of a sealing water without installing a sealing water detection means for detecting te oscillation of the sealing water.

In the urinal flushing device A, a catch basin 8 is disposed at an opening section 1d on the bowl section 1b side of a trap 1a which forms the sealing water 1c for preventing odor from rising by accumulating flushing water therein. The catch basin 8 includes a microwave damping characteristic or a microwave cutting characteristic which reduces the output level of a doppler signal 24 due to the oscillation of the sealing water 1c to a value smaller than the threshold level for human body detection within a frequency range for human body detection.