A novel tripeptide compound represented by the following general formula (I) exhibiting superior HIV protease inhibition activity, and an anti-AIDS medicine comprising this compound as an effective component and a pharmaceutically acceptable salt thereof. ##STR1## (R)-N-(2-methylbenzyl)-3-{(2S,3S)-3-[N-(2-chromonecarbonyl)-L-asparaginyl]a mino-2-hydroxy-4-phenylbutanoyl}-5,5-dimethyl-1,3-thiazolidine-4-carboxamid e can be given as a typical example of this compound.