PURPOSE: To prevent a seal member from burning by releasing the seal member of a closed body from shearing stress in closing operation and additionally protecting the radiation of crystal at a high temperature during pulling operation at an apparatus for pulling crystal.

CONSTITUTION: The seal member is constituted as a gasket 9 to be burdened mainly by pressure without shearing stress and friction and the seal member is protected from the heat radiation of the crystal at a high temperature by a guard 15 during the pulling of the crystal. Thereby, the using life of the gasket 9 is prolonged without requiring a cost for technique and as an operating period is kept longer as the result to economically prepare the crystal to be pulled compared with conventional technique.