<p>A dust detector in a vacuum cleaner (1) includes a light-emitting element (7) exposed into a dust suction passage for emitting a light beam into the dust passage (4), and a light-detecting element (8) exposed into the dust suction passage for detecting the light beam emitted from the light-emitting element. A detector unit detects the amount of dust flowing through the dust suction passage based on the intensity of the light beam transmitted from the light-emitting element across the dust suction passage to the light-detecting element. The light-emitting element and the light-detecting element are covered respectively by a pair of light-transmissive covers (9, 10) having respective end faces exposed into the dust suction passage and lying flush with an inner wall surface (4a) of the dust suction passage.</p>
