[Problem to be Solved] An immunostimulant highly safe and administrable for a long period of time as well as a pharmaceutical composition containing the immunostimulant as an active ingredient and drink or food products for immunostimulation are developed and provided. [Solution] An immunostimulant containing a compound represented by the following general formula (I) or a pharmaceutically acceptable salt thereof as an active ingredient is provided. R1 is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, R2 to R5 are independently a hydrogen atom, or a substituted or unsubstituted lower alkyl or lower acyl group, X is &mdash；(CH2)2&mdash；, &mdash；(CH2)3&mdash；, &mdash；(CH2)4&mdash；, &mdash；CO&mdash；CH2&mdash；, &mdash；CO&mdash；(CH2)2&mdash；, &mdash；CO&mdash；(CH2)3&mdash；, &mdash；CH2&mdash；CO&mdash；CH2&mdash；, &mdash；CO&mdash；O&mdash；CH2&mdash；, &mdash；CO&mdash；O&mdash；(CH2)2&mdash；, &mdash；O&mdash；CO&mdash；CH2&mdash；, &mdash；O&mdash；CO&mdash；(CH2)2&mdash；, &mdash；CH2&mdash；O&mdash；CH2&mdash；, &mdash；CH2&mdash；O&mdash；(CH2)2&mdash；, &mdash；O&mdash；CH2&mdash；, &mdash；O&mdash；(CH2)2&mdash；, &mdash；O&mdash；(CH2)3&mdash；, &mdash；NHY&mdash；CO&mdash；CH2&mdash；, &mdash；NHYCO&mdash；(CH2)2&mdash；, &mdash；CO&mdash；NHY&mdash；CH2&mdash； or &mdash；CO&mdash；NHY&mdash；(CH2)2&mdash；, Y herein is a hydrogen atom or a lower alkyl group.
