An object is to provide a capsule endoscope which allows an observation while floating on a liquid with a low specific gravity in total in an inside of a subject body without impairing an insertion property into the subject body even in including contents whose specific gravity is high. A shape memory alloy spring (14) presents a memorized shape of causing a volume changing unit (13) to be displaced to a storage position where the volume changing unit (13) is stored in a capsule casing (11) based on a body temperature of the subject body when the capsule endoscope is inserted into the subject body, so that a size not impairing the insertion property into the subject body can be realized. After the insertion into the subject body, water (3) is fed appropriately into the subject body and the shape memory alloy spring (14) then presents, based on a temperature of the water, a memorized shape of causing the volume changing unit (13) to be exposed to an outside of the capsule casing (11) and to be displaced to an exposure position where a volume of the casing is increased, so that the volume changing unit (13) can be displaced to the exposure position while absorbing an outer air into the inside from a ventilation hole (13a) in the subject body, the volume of the casing is increased, and an observation with the capsule endoscope floating on the water (3) can be performed due to a low specific gravity in total even in including contents (12) whose specific gravity is high.
