To provide a filter mounting structure that allows a filter to be installed to a filter casing through a simple operation.

The filter mounting structure is composed of a slide body, a fixing member for regulating the slide body so as to be slidable, a filter pressing member and a connection member for connecting the slide body, the fixing member and the filter pressing member in this order. The slide body includes a first long hole long in a direction oblique with respect to a filter pressing direction. The fixing member includes a second long hole long in the filter pressing direction. The connection member is inserted in the first and second long holes, and fixed to the filter pressing member, so that the filter pressing member moves in an air inflow or outflow direction of the filter casing to press the filter to the filter casing by sliding the slide body while regulating it by the fixing member.