Emotion plays an important role in goal-directed behavior. Although numerous neuroimaging studies have been conducted, the neural mechanisms behind emotion generation and regulation are still elusive. This is partly explained by large individual variations in emotional responses in addition to the fact that emotion is a complex process. The present functional magnetic resonance imaging study aimed firstly to specify valence-dependent brain activation, and secondly to clarify the interactions between the regions underlying emotional processing. We measured brain activation in 12 healthy adults while passively viewing affective pictures. The individual valence ratings were negatively correlated with activation in the frontal, parietal, occipital lobes, and in the subcortical regions including the amygdalae. The parametric mediation analysis performed on these regions showed that the right ventrolateral prefrontal cortex (Brodmann area 47) was main mediator of the valence ratings with other regions. Interestingly, there was no mediator region for the ventrolateral prefrontal cortex. These results indicated the possibility that the right ventrolateral prefrontal cortex mainly participated in the integration of visually induced emotional processes in the valence dimension.