The disclosure provides a technology for efficiently introducing a foreign substance into at least cytoplasm of eukaryotic cells from outside the cells. The method disclosed here for introducing a foreign substance of interest in vitro or in vivo into at least cytoplasm of eukaryotic cells from outside the cells includes (1) a step of preparing a foreign substance introduction construct including a carrier fragment composed of KKRTLRKSNRKKR (SEQ ID NO:1) and the foreign substance of interest linked to the N-terminal and/or C-terminal side of the carrier peptide fragment; (2) a step of supplying the foreign substance introduction construct to a sample containing a target eukaryotic cell; and (3) a step of incubating the sample, to which the foreign substance introduction construct has been supplied, to thereby introduce the construct into the eukaryotic cell in the sample.