A cell observation information processing system comprising a computer, which comprises: a tag acquiring section configured to acquire, as a search tag for searching for observation information that has been acquired via an observation information acquiring section in response to an acquisition order at one time point to carry cell observation results including at least one of a cell image and activity data indicating cell activity by at least one of a number of cells, cell confluency, morphology and viability, a tag set including at least one of a tag indicating user identifying information for identifying a user who conducts cell observation, a tag indicating cell identifying information for identifying cells under observation, a tag indicating date/time information for identifying a date/time when the observation information was acquired, a tag indicating information on user's work for cell maintenance, a tag indicating apparatus identifying information for identifying an apparatus used in acquiring the observation information, a tag indicating activity data variation information and an image tag for indicating the cell image; and a storing section configured to assign, as a search tag, the tag set acquired by the tag acquiring section to the observation information, which has been acquired via the observation information acquiring section in response to an acquisition order at each time point, and store search-tagged observation information, to which the search tag has been assigned, into an archive section, wherein the tag acquiring section is configured to automatically generate a possible tag set as an m-th tag set to be assigned to an m-th piece of observation information acquired via the observation information acquiring section in response to an acquisition order at an m-th observation time point, on a basis of a cell image contained in the m-th piece of observation information, where m is an integer equal to or greater than 1, accept an order by the user regarding a change from the possible tag set automatically generated to another tag set, and, if having not received from the user an order that a change to another tag set should be made, acquire the possible tag set automatically generated as the m-th tag set without accepting an input of another tag set by the user or, if having received from the user an order that a change to another tag set should be made, accept an input of another tag set by the user and acquire the accepted another tag set as the m-th tag set. a tag acquiring section configured to acquire, as a search tag for searching for observation information that has been acquired via an observation information acquiring section in response to an acquisition order at one time point to carry cell observation results including at least one of a cell image and activity data indicating cell activity by at least one of a number of cells, cell confluency, morphology and viability, a tag set including at least one of a tag indicating user identifying information for identifying a user who conducts cell observation, a tag indicating cell identifying information for identifying cells under observation, a tag indicating date/time information for identifying a date/time when the observation information was acquired, a tag indicating information on user's work for cell maintenance, a tag indicating apparatus identifying information for identifying an apparatus used in acquiring the observation information, a tag indicating activity data variation information and an image tag for indicating the cell image; and a storing section configured to assign, as a search tag, the tag set acquired by the tag acquiring section to the observation information, which has been acquired via the observation information acquiring section in response to an acquisition order at each time point, and store search-tagged observation information, to which the search tag has been assigned, into an archive section, wherein the tag acquiring section is configured to automatically generate a possible tag set as an m-th tag set to be assigned to an m-th piece of observation information acquired via the observation information acquiring section in response to an acquisition order at an m-th observation time point, on a basis of a cell image contained in the m-th piece of observation information, where m is an integer equal to or greater than 1, accept an order by the user regarding a change from the possible tag set automatically generated to another tag set, and, if having not received from the user an order that a change to another tag set should be made, acquire the possible tag set automatically generated as the m-th tag set without accepting an input of another tag set by the user or, if having received from the user an order that a change to another tag set should be made, accept an input of another tag set by the user and acquire the accepted another tag set as the m-th tag set.