To facilitate a vent plug by easily scraping out a bulky sand with brush, etc.

In the vent plug 10 fitted to a mold for forming a sand mold and venting the air in the mold at the time of pressing the sand in the mold, partition plate parts 13 for partitioning the inner part and the outer part of the mold, slits 12 formed in the partition plate parts 13 and dischargable of the air in the mold and recessed parts 13m arranged along the opening parts of the slits 12 so that the bulky sand S inserted deeply into the slit 12 forms wide at the front surface side of the partition plate parts 13 in contact with the sand in the mold. In this way, the bulky sand S inserted deeply into the slit 12 is supported at the portion SW widened at the surface side, with the partition plate parts 13. Therefore, the bulky sand S is not pushed further deeply into the slit 12 even in the case of being pushed with the brush etc. Further, since the contacting area of the bulky sand S with the brush, becomes large, the bulky sand S is easily scraped out with the brush.