To provide a TE01 mode microwave exciter having a compact and simple structure.

In the liquid level measuring microwave exciter for measuring the liquid level by radiating a microwave in a circular waveguide tube, a radial waveguide 4 is formed in which first and second circular or polygon flat conductive plates 1, 2 mutually in parallel are short-circuited at a periphery 3. The top end of a power feeding input line 5 connected to the center of the first flat conductive plate is made to face the center of the radial waveguide. Two or move pairs of slots 7, 7 elongated in a radial direction for radiating an electric field in circumferential direction are provided in an axially symmetrical way at the second flat conductive plate. At the same time, disturbing elements 8, 8 for disturbing the electromagnetic field in the radial waveguide and coupling the magnetic field with the slot antenna are provided near to the slot antenna, so that TE01 mode microwave is radiated into the circular waveguide tube connected in the same axis as the radial waveguide.