The mutifilamentary $Nb_3$Sn wire containing 135 Nb filaments was manufactured by the internal tin method. The critical current density ($J_C$) in magnetic fields for the wires heat-treated at $660^{/circ}C$ and $700^{/circ}C$ were investigated. The Non-Cu $J_C$ and n-value of 0.82 mm$phi$ $Nb_3$Sn wire heat-treated at $700^{/circ}C$ for 240 hours was approximately 450 A/$mm^2$ at 12T, 4.2K and 14, respectively. Also the $B_{C2}$ of $Nb_3$Sn wire extrapolated by Kramer plot was 27.2T. The wire heat-treated at $700^{/circ}C$ for 240 hours showed smaller residual tin concentration in the matrix and the larger area of $Nb_3$Sn layer as comparison with the wire heat-treated at $660^{/circ}C$.