Display device and display optical system unit

A display apparatus comprising:

• a reflecting type light valve which has a light incidence/reflection surface;
• a drive circuit which drives said reflecting type light valve by supplying an image signal;
• a cooling system which cools at least said reflecting type light valve with cooling fluid;
• and
• a partition wall which partitions a space in said display apparatus into a cooling fluid side having a cooling fluid path and a light incidence/reflection surface side having a light incidence/reflection path;
• wherein said reflecting type light valve forms a part of said partition wall, and said light incidence/reflection surface faces said light incidence/reflection surface side;
• wherein the cooling fluid path and the light incidence/reflection path differ from one another without crossing one another;
• and
• wherein a part opposite to said light incidence/reflection surface of said reflecting type light valve is cooled by said cooling system.