An injection-molded plastic component can be directly joined with a metal plate whose surface is micro/nano-structured. The direct joining is achieved in a mold at the same time as a plastic component is formed by the injection molding. The joining performance, such as joining strength, can be affected by states of flowing polymer melt during injection molding; especially, temperature can have strong effect. Controlling high/low temperature simply is, however, not sufficient for the direct joining. Further understanding of the effect of temperature motivated us to develop an advanced system controlling mold temperature. The present study dealt with controlling distribution of mold temperature as the new system. The effect of the distribution on joining strength of a metal-polymer hybrid component was investigated. To actively control the distribution of temperature, we developed a mold that was equipped with some separated local heaters. The individual heaters can control the temperature of the assigned areas of the mold surface. Using the mold, we considered two types of temperature distributions. In the one condition (condition-I), the temperature of a pocket for a metal insert plate (Tm: temperature of metal) was higher than that of the polymer flowing part, such as a runner and a cavity, (Tp: temperature of polymer). The other one (condition-II) was opposite; Tm was lower than Tp. The produced joints were evaluated by the tensile shear test. The results showed that Tm is dominant for the joining strength. In the condition-I (Tm > Tp = constant), the joining strength increased with the increasing of Tm. On the other hand, in the condition-II (Tp > Tm = constant), the strength never varied with the change of Tp. These results let us assume that the temperature of not polymer melt itself but a metal-polymer interface is important for the formation of the joining; that is, the temperature of the microstructure, which the melt infiltrates into, is important.