It was built in 1954 by the company OESA from Azpeitia (province of Guipuzcoa) thanks to a legacy of Fermín De Lasala, Herzog of Mandas. This instrument is complemented with a choir organ installed in the chancel (Eco). Both instruments are playable simultaneously from the respective console thanks to the electric action.

In 2007 it was reinaugurated after a comprehensive restoration by Bernal-Korta from Azpeitia. In the course of this restoration the basic characteristic features of this beautiful instrument were respected, nevertheless the old console was substituted by a new one with a state of the art combinator.

It has five manuals with a span of 61 keys (C-c4) and pedal with 30 keys (C-f1). The total number of stops is 125.