Ventilating fan

A ventilating fan, comprising:

• a frame which has a bottom surface formed with an air inlet and a side surface provided with an air outlet;
• a casing in which a fan motor is mounted;
• and, an adapter fitted to an air outlet of the casing, wherein first flangings are extended outwards from both vertical side edges of an air inlet of the adapter, second flangings are extended outwards from both horizontal side edges of the air inlet of the adapter, outer edges of the first flangings are firstly bent towards the casing side to form both side surfaces perpendicular to the first flangings, and then edges of the both side surfaces are bent towards each other to form edge surfaces, and, the first flangings, the side surfaces, and the edge surfaces confine open grooves;
• one or more protrusions are disposed on an outer periphery of the air inlet of the adapter near the first flanging or the second flanging, and a slot is formed between the one or more protrusions and any one of the first and the second flangings;
• first folded sheets are extended outwards from both vertical side edges of the air outlet of the casing;
• and
• an edge of the air outlet of the frame abuts against and is clamped in the slot such that the adapter is locked to the frame, and the first folded sheets are insertable into the open grooves of the adapter from below upwards.