An optical block, which may be of a small size, for applying light efficiently to a display device such as a liquid crystal panel, and a display apparatus. The optical block (1) has a polarizing beam splitter (3) mounted on baseboard (2) at a predetermined angle with respect to light applied from a light source (10), for passing a P wave toward an exit side and reflecting an S wave, reflecting device (4) mounted on the baseboard (2) for reflecting the reflected S wave toward the exit side, and plane-of-polarization rotating device (5) mounted on the baseboard (2) for rotating the plane of polarization of the S wave reflected toward the exit side. The display apparatus has a light source (10), a first multilens array (12), the optical block (1), a second multilens array (13), separating device (14, 19) for separating emitted light into red light (R), green light (G), and blue light (B), light modulating device (17, 21, 26) for generating modulated red light, modulated green light, and modulated blue light based on the separated light, and emitting device (18) for combining the modulated red light, modulated green light, and modulated blue light and emitting combined modulated light. The optical block is of a thin structure so that it may be a space saver and lightweight. Optical paths from the light source to liquid crystal panels or the like may be reduced to reduce the size of the display apparatus.