[Problem] A baseboard and extension modules can be connected without the use of lead lines connected between the baseboard and extension module.[Solution] A baseboard includes first connectors; an extension module includes a second connector that fits with the first connectors; the first connectors and the second connector include ground terminals, source terminals, and signal terminals connected to signal lines; each of the ground terminal, each of the source terminal, and each of the signal terminals constituting a suit of terminals, a plurality of the suit constituting the first connectors; the ground terminals, the source terminals, and the signal terminals disposed at a constant pitch on the baseboard; the second connector including a suit of terminals, the suit including a ground terminal, a source terminal, and a signal terminal; and the baseboard and the extension module are directly connected only by the first connector and the second connector.