Provided is a liquid crystal display device includes an optical switching member; a light guide plate made of a thermoplastic material, which includes at least one light introducing portion on at least one side surface thereof; and a light source disposed on the at least one side surface, in which: the at least one light introducing portion includes, in plan view of the light guide plate: a first portion extending from a light incident surface, which is an end surface of the at least one light introducing portion, while keeping a substantially constant width; and a second portion, which extends from the first portion and has a form which widens; and at least the second portion is connected to a front surface of the light guide plate through an inclined surface which is smoothly continuous with the front surface of the light guide plate.