[piusv]

This is from the Lateran Council which is a general or ecumenical council. According to Catholic Encyclopedia:

All the arguments which go to prove the infallibility of the Church apply with their fullest force to the infallible authority of general councils in union with the pope. For conciliary decisions are the ripe fruit of the total life-energy of the teaching Church actuated and directed by the Holy Ghost.

So, yes, it is infallible. You can read more in the Catholic Encyclopedia online.

[daniel1212]

All the arguments which go to prove the infallibility of the Church apply with their fullest force to the infallible authority of general councils in union with the pope. For conciliary decisions are the ripe fruit of the total life-energy of the teaching Church actuated and directed by the Holy Ghost.

Which premise of ensured perpetual magisterial infallibility (when speaking according to the infallible scope and subject-based criteria) is novel, unnecessary and unScriptural. You are welcome to try to defend it, and your basis for assurance of the veracity of this doctrine.