PURPOSE: To inspect signals fed to the applicable device through an external wiring by shutting the external wiring from the device side electrically in the condition that the external wiring is in connection.

CONSTITUTION: The first block 1 for inner line terminal and the second block 5 for outer line terminal are provided, and the second block 5 is inserted to the first block 1. The base 2 of the first block 1 is formed in thin rectangle from an insulative material having a projection in the center of the undersurface, and each inner line terminal 3 is a plate-shaped metal piece in an inverted L-form, and a plurality of such terminals 3 are laid along a straight line stretching in the longitudinal direction of the base 2 while the vertical portion of the inverted L-form is penetrating. The base 2 is a plastic molding in which the inner line terminal 3 is embedded. The base 6 of the second block 5 is formed in a thin and long cylinder of an insulative material having a rectangular section which is missing in the middle part of the bottom member, wherein a partitioning plate is installed upright on the oversurface. The outer line terminal 7 is a plate-shaped metal piece of resilient material assuming a J form and is fixed in each division of the base 2 divided by the partitioning plate together with a screw 8.