Since horses (Equus caballus) domesticated 5500 years ago, humans and horses have built a closed relationship.“Jinba Ittai”expresses this relationship, and it means “a feeling as if hearts of a human and a horse are united”. What kind of a sense is a “Jinba Ittai”actually, when a human is in contact with a horse? What kind of processes occur the sense of “Jinba Ittai”? In present study, we examined “Jinba Ittai”which persons with experience of equestrian in training of horses for using interviews for them. In addition, we used M-GTA, which is the one of the qualitative analysis and focuses on the processes until a subjective sense occurs. The results showed that “Jinba Ittai”is a sense of operation agency (“It seems like the horse has become my limbs”) and a sense of smooth interaction (“We understand each other very well”). Additionally,we revealed that when a horse responds to instructions of a human immediately (i.e.,improved operation sense), the human feel “Jinba Ittai”. These results suggested that when the responses of other agent (such as horses) are produced immediately after the own responses, humans feel “Jinba Ittai”with the sense of smooth interaction.