Waveguide connecting structure, waveguide connector, waveguide unit, mode converter, imaging device, and endoscope

A waveguide connecting structure of connecting a first waveguide to a second waveguide, or to a transmitting and receiving device, the waveguide connecting structure comprising:

• an elastic body configured to cause an external conductor to closely contact a dielectric body, the external conductor and the dielectric body being included in the first waveguide configured to transmit radio waves having a frequency of millimeter waves or higher, the external conductor covering an outer periphery of the dielectric body;
• and
• a three-dimensional body configured to hold the dielectric body of the first waveguide, and the second waveguide or the transmitting and receiving device, the second waveguide being different from the first waveguide, the transmitting and receiving device being configured to transmit and receives radio waves,
• the three-dimensional body having electric conductivity inside an insertion hole holding the first waveguide, and
• the external conductor of the first waveguide including a radially spread portion that has been radially spread, the radially spread portion being where the first waveguide and the three-dimensional body are connected to each other.