Recently, for electronic devices operating at high frequencies, the suppression of a high-frequency electromagnetic field of 1GHz or more has become necessary. We focus on a loose connector between a pair of electrical devices operating in the high-frequency band. Many electronic devices are used in living spaces, most of which are connected to one another. When a user connects two devices, achieving good contact only by finger tightening can be difficult. Accordingly, in this paper, considering the case where the tightening torque of a coaxial connector is insufficient, we analyze the effect of loose contact on electromagnetic field radiation from a transmission line.