PURPOSE: To facilitate fitting or replacing of a filter and also enhance reliability by making an axial length of an elastic filter longer than a hollow portion in a second air cleaner.

CONSTITUTION: A second air cleaner 1 comprises a hollow member 4 and an elastic filter 6. It is connected to a negative pressure servo carburetor so that cleaned air is introduced to keep a lower chamber of diaphragm below the atmospheric pressure. Axial length of the elastic filter 6 is about 1/4 longer than a hollow 10 formed in an inner case 7 of the hollow member 4. When the elastic filter 6 is inserted in the hollow 10, it thus protrudes from an air inlet 16 of the hollow member 4 by an amount of a longer portion 6a. Accordingly, even when the elastic filter 6 is inserted into the hollow 10 under being bent, the adjustment in bend is possible by holding a protrusion portion 6a. Fitting of the elastic filter 6 is made suitably, without a gap, in a short time. And also, replacement of the elastic filter 6 is simplified. When dirt 17 sticks at the air inlet 16, it does not enter the cleaner.