A focus adjustment device for adjusting a focus state of a projection lens unit in an image projection apparatus is provided. The focus adjustment device includes a focus adjustment member rectilinearly movable in a first direction; a rotational shaft; a first movement-converting member for converting a rectilinear movement of the focus adjustment member into a rotary movement of the rotational shaft; and a second movement-converting member for converting the rotary movement of the rotational shaft into in a rectilinear movement of the projection lens unit along a focusing direction.