The present invention relates to a test instrument (X) including a capillary (5) for moving a sample liquid (B), a liquid pooling portion (4) communicating with the capillary (5) for retaining the sample liquid (B) to be introduced into the capillary (5), and a liquid introduction selector (12) for selecting whether or not the sample liquid (B) retained in the liquid pooling portion (4) is introduced into the capillary (5). The present invention also relates to an attachment provided with the test instrument (X), and a concentration measuring apparatus to which the attachment is mounted for use.