Confinement of light quarks in QCD at finite density

The 4q effective Lagrangian and the gap equation are derived for light quarks in the confinement phase of QCD. The modification of the confining string due to finite quark density (chemical quark potential \mu) is observed. As a surprising result in a multiquark system with a common string junction an attractive well appears of radius \mu/\sigma and of an average depth equal to \mu. Possible implications for the density phase transition are discussed.