This study explores the differences between Facebook and Instagram use by investigating the influence of technology attributes (visualizing elements, the friend recommendation algorithm, privacy settings, openness, perceived ease of use and usefulness), individual factors including innovativeness and motivations/gratifications (social interaction, entertainment, peeking, passing time, need for recognition) in using Facebook and Instagram, and socio-cultural factors (subjective norms, SNS culture) on the general use and use change of both sites. Whether and what kind of different characteristics of using the both platforms exist between younger and older generations were also examined. The findings of the current study indicate that individual, technological, and socio-cultural factors differently influenced individuals’ Facebook and Instagram use. Among the technology attributes, visualizing elements were positively related to Instagram use, and the friend recommendation algorithm was a positive predictor of using Facebook. In terms of the individual factors, while Facebook users were likely to utilize it to get a good reputation and to access it when they want to spend time alone, Instagram users tended to employ it for entertainment. SNS culture, which refers to using Facebook (or Instagram) because it is part of the culture of one’s generation, was the only socio-cultural factor that had a significant relationship with Facebook use. Generational differences of the proposed factors influencing Facebook and Instagram use were also found. More specifically, Instagram’s visualizing elements were the only significant predictor of use by younger generations; older people tend to use Facebook and Instagram for passing time and to fulfill their need for recognition. The findings of the current study expand the theoretical frameworks of the technology acceptance model (TAM), uses and gratifications (U&G), the theory of reasoned action (TRA), and the theory of planned behavior (TPB) by revealing how perceived ease of use and usefulness can differently activate the level and change of Facebook and Instagram use; which motivations/gratifications can significantly stimulate the two stages (general use and use change) of Facebook and Instagram use; and how subjective norms differently influenced level of using Facebook or Instagram. Further specific findings will be valuable assets for practical social media industries.