  We consider the $\Theta^+(1540)$ pentaquark in the string model that
correctly reproduces the linear Regge trajectories for the case of orbital
excitations of light $q\bar q$ mesons and $qqq$ baryons. Assuming (and arguing
in favour of) the diquark-antiquark-diquark ($[ud]\bar s [ud]$) clustering of
this orbitally excited object we found its mass about $290 \rm {MeV}$ above the
experimental value $1540 \rm {MeV}$. In the model considered this discrepancy
could be attributed to the change of the constituent mass of $\bar s$ antiquark
as compared to that of $s$ quark localized at the string end.
