A jack device includes an insertion portion configured to receive a plug through an open end along a first axis. The insertion portion has an opening and a terminal. The opening has a predetermined depth from the open end to an inside of the insertion portion. The opening has a first inner surface that is increasingly away from the first axis from the inside to the open end, and a second inner surface whose distance from a certain point on the first axis is shorter than a distance between the first inner surface and the certain point. The terminal is located further inside than the opening in a direction of the first axis and is opposite to the second inner surface in a direction crossing the first axis. The terminal comes into pressure contact with the plug when the plug is inserted into the insertion portion.