PURPOSE: To connect directly an image type line by providing a choke consisting of a slot line of 1/2 wavelength to a connection boundary part of two image type slot lines made of a microwave plane circuit.

CONSTITUTION: A choke citcuit 9 made of the slot line having 1/2 wavelength in total is provided to the connected part of the two image type slot lines 7, 8 made of the microwave plane circuit constituted by a conductor plate clipped by split waveguides. The impedance of the choke citcuit goes to zero when it is viewed from a connecting point P of the slot lines 7, 8. Thus, even if there is a gap at the connection part of the image type slots 7, 8, the gate is short-circuited and since no electric discontinuity is produced at the boundary, the image type slot lines 7, 8 are connected directly.