A lamp receptacle of a projection apparatus includes a receptacle body defining a receiving space, and having a peripheral wall and an upper opening. The peripheral wall is formed with an aperture. A fixing element is attached securely to the peripheral wall above the aperture, and protrudes into the receiving space. A filter glass is disposed in the receiving space behind the aperture in the peripheral wall. A holding frame is disposed behind the filter glass, and has a central hole aligned with the aperture. A mounting arm has a vertical section integrally formed with an upper section of the holding frame, and a horizontal section extending frontward from the vertical section to overlap and fasten the upper fixing element, thereby retaining the holding frame in such a manner to urge the filter glass to abut against the peripheral wall around the aperture.