To provide a projection display apparatus that allows adaptive selection of a network communication mode while suppressing cost increase.

The projection display device includes: a LAN signal processing circuit part 402 for performing communications over a network; a linkage connector 403 that is connected to a functionality expansion unit 50 with more advanced processing capability than that of the LAN signal processing circuit part 402. A control part 407 operates the LAN signal processing circuit part 402 when the functionality expansion unit 50 is not connected to the linkage connector 403. Meanwhile, the control part 407 operates the functionality expansion unit 50 when the functionality expansion unit 50 is connected to the linkage connector 403.