Abstract: A microscope system includes: a main body portion having an optical system for forming an image from at least observation light from a specimen; an objective lens unit having an objective lens for taking in the observation light and having a base portion with an approximately belt shape for holding the objective lens on one end; and a unit attachment portion that is held by the main body portion and is configured to detachably attach the base portion at a position where at least an optical axis of the objective lens coincides with an optical path of the observation light.

Abstract: A microscope system includes: a main body portion having an optical system for forming an image from at least observation light from a specimen; an objective lens unit having an objective lens for taking in the observation light and having a base portion with an approximately belt shape for holding the objective lens on one end; and a unit attachment portion that is held by the main body portion and is configured to detachably attach the base portion at a position where at least an optical axis of the objective lens coincides with an optical path of the observation light.

Abstract: In an in vivo microscopic observation method of the inside of the body of an experimental small animal using a stick type objective for an optical microscope, the determination of an observation site in the inside of the body of the animal and the checking of the position of the field of view of the objective can be done without significant increase of the burden of the tested animal. In the inventive method of the microscopic observation of a tissue or a cell in the inside of the body of a small animal, an endoscope is inserted through a first small hole opened in the epidermis site of the small animal; a second small hole piercing through the epidermis of the small animal is opened based on an image of the endoscope; and a thin diameter lens unit of the stick type objective is inserted in the second hole.