Abstract: A drive pulse for emitting and turning-off a light emitting element is output, the level difference or the level ratio between the light emission zero point detection signal from a light receiving element having received the light from the light emitting element and a putting-off zero point detection signal from the light receiving element when the light emitting element is put off is calculated, and the level difference or the level ratio is compared with a preset level to thereby determine the abnormality of the light emitting element, the light receiving element and a peripheral circuit. With this arrangement, even if the ratio of noise light occupied in the zero point output is reduced, whether detecting elements and the peripheral circuit are good or bad and whether the elements are abnormally polluted or not can be reliably tested without the effect of the dispersion of the detecting elements and the change of an ambient temperature, whereby the reliability of a smoke detector is improved.

Abstract: A static pressure slide unit includes a guide rail, two-part slider slidably mounted on the guide rail and having a slider main body and a slider pressure member, and a mechanism interposed between the slider main body and the slider pressure member for constantly urging the slider pressure member against the guide rail. A pressurized fluid supplying system is also provided for supplying a gas or liquid under pressure to a sliding contact interface between the guide rail and the slider.