Confocal microscope

A confocal microscope for observing a surface of an object by focussing irradiated light from a point light source on the surface of said object with an objective lens, splitting a part of reflected light from said object with a first beam splitter so as to make it pass through a first diaphragm, and focusing light that has passed through said first diaphragm on a first light detector, said confocal microscope comprising,

• a second beam splitter provided between said first beam splitter and said first diaphragm,
• a third beam splitter for splitting further light split with said second beam splitter,
• a second diaphragm disposed in a vicinity of a focal point position of light split with said third beam splitter,
• a second light detector for detecting light that has passed through said second diaphragm
• a third diaphragm disposed in a vicinity of a focal point position of light that has passed through said third beam splitter,
• a third light detector for detecting light that has passed through said third diaphragm,
• a comparator for comparing a quantity of light detected by said second light detector and a quantity of light detected by said third light detector, and
• a driving mechanism for controlling the position of said object in accordance with an output from said comparator, wherein
• the layout relationship among said second beam splitter, said third beam splitter, said second diaphragm, said second light detector, said third diaphragm, and said third light detector is such that a difference between a quantity of light detected by said second light detector and a quantity of light detected by said third light detector becomes a predetermined quantity when light is focussed on the surface on said first light detector, while when light is not focussed on the surface of said first light detector, the layout relationship is such that the difference between the quantity of light detected by said second light detector and the quantity of light detected by third light detector is a quantity of light that is different from said predetermined quantity, and said driving mechanism is adapted to control the position of said object such that an output from said comparator becomes said predetermined quantity.