PURPOSE: To provide a filter apparatus where the fitting of a filter medium is made simple and the wear and damage to the filter medium on rolling is made small irrespective of the variation in the thickness of the filter medium and the filter medium is always kept in the adhering condition to the air outflow surface of the equipment body.

CONSTITUTION: Slots 7, 7 are arranged almost in the shape of a truncated chevron to an air outflow surface 2 of an equipment body 1 and are at an angle of 15-50° to the air outflow surface 2. The ends of guide rolls 4a, 4b are inserted in the slots 7, 7 respectively with a play and tractive force when rolling a filter medium X is applied to each of guide rolls 4a, 4b to move to the air outflow surface 2 side of the equipment body 1. As a result, the filter medium X is always kept in the adhering condition to the air outflow surface 2 of the equipment body regardless of the thickness of the filter medium X.