The Sanmon was set up in Kanen3 (1750) cost 3,788-Ryou when it was after the 43 years to main hall erected.
It is with a width of 20.398 meters, a height of 20.448 meters and a depth of 7.999 meters. The roof of its has an area of 883.972 square meters.

It is a stately double-gate which has five-column spacing , three-areaway and the two-storey roofed with the HIWADA and designated as a Nationally Important Cultural Property at October 1965(certificate No.1596).

On the second pavilion, there are the Manjusri who generates the wisdom at the center, on every his side, the four heavenly kings who bring good luck, the mural which shows white lotus and the fan light formed an image of Kishoutennyo, to give expression to the world of Buddha.

The nameplate "Zenkoji" known for HATOJI (pigeon logo ) was written by Rinnouji-Monseki-KoujunShinnou and run up in Tempo 3 (1830).

From the galleria, it is the spectacular scenery to keep a close eye on the development of Nagano.

In the ordinary , it was fixed in conjunction with the repair of the main hall. At first , it had a shingle-roof. Then , as the main hall was roofed with the HIWADA , the roof of the Sanmon has been made with the HIWADA since Dec.1921 (Taishou10).

In Showa 48 (1973) , It was re-loafed with HIWADA and put the lightning rod. The stone-stairway and the paving tone was mended in Showa 58 (1983) .

However it stood out the cumulative degradation , to tilt pillars and to deform the axial . And the HIWADA-roof also needed to repair in near future. So the Zenkoji suggested to do the first-time thorough repairs to obtain the permission of the Cultural Affairs Agency , the prefecture and the city of NAGANO after the Heisei9-Okaicyo(1997).

Now It has been undergone with great cordiality to explore the damage completely.