In 96 A.D. Roman Emperor Domitian was assassinated and M. Cocceius Nerva, an old Italian noble, was proclaimed emperor. But about one year later, Nerva adopted a Spanish general, M. Ulpius Traianus (Trajan) and nominated him as his coruler. Most scholars consider that this adoption is one of the most significant events in the history of the principate, because it inaugurated a new system of succession (Adoptivkaisertum). One of them regards it as an expression of the Stoic ideal, another one considers that by accepting this system the principate was reconciled with the philosophy which had opposed Nero and the Flavian Emperors. In the Panegyric, however, Pliny the younger insisted that the important point about this adoption was not the method but the person adopted. And he described Nerva as a helpless old man and a tool of the God for Trajan's adoption. How are we to understand his opinion? In this paper we have tried to clarify the political process to this adoption and Pliny's political position under Nerva. Our arguments are as follows. As a candidate for Nerva's successor, Trajan had a rival whose career G. Alfoldy and H. Halfmann reconstruct. His name is M. Cornelius Nigrinus Curiatius Maternus. He was connected with Domitianic senators and perhaps the praetorian prefect, Casperius Aelianus. In the summer of 97, Casperius and his troops rose in revolt to avenge Domitian. Succumbing to their demands, Emperor Nerva had a tendency gradually to agree with Nigrinus and Domitianic group. But this political situation was changed by L. Licinius Sura. He made Nerva's final choice fall upon Trajan. (We must make much of Epitome de Caesaribus XIII, 7; it means not Sura's proposal but his real political maneuvering.) Therefore, in the process to the adoption we can find neither new system nor philosophical principle. We can see only a scramble for political power. Then, by our interpretation on the political process, we can explain the political position and opinions of Pliny. He was one of the anti-Domitianic senators. He accused a Domitianic senator, Publicius Certus who was supported by Nigrinus. So Pliny was helped by the adoption and nomination of Trajan (not Nigrinus). He couldn't praise Nerva except for the final choice, because Nerva had leaned toward Pliny's political opponents for a while. These personal affairs influenced his opinions on the adoption and the picture of Nerva in the Panegyric.