Waveguide slot antenna and warning system using same

Provided is a waveguide tube slot antenna (A), including: a waveguide tube (10) having a transverse section having a rectangular shape in each part of a waveguide (2) in an extending direction thereof; and a plurality of radiating slots (3) arranged in the waveguide tube (10) at predetermined intervals, in which: the waveguide tube (10) includes a first waveguide tube forming member (11) and a second waveguide tube forming member (12) each having the transverse section having a shape with an end, the first waveguide tube forming member (11) and the second waveguide tube forming member (12) being configured to define the waveguide (2) by being coupled to each other; and the first waveguide tube forming member (11) is formed to have a flat shape and includes the plurality of radiating slots (3).