To provide a gate valve device preventing deterioration of a seal member due to radicals even if it is used in a high temperature environment.

The gate valve device has: a valve element seated on a valve seat 63 with a predetermined distance to the valve seat 63 for blocking an opening part; and a seal member for sealing between the valve element and the valve seat when the valve element is seated on the valve seat. The seal member has: a first seal part 58 elastically deformed by receiving a reaction force acting from the valve seat by pressing the valve seat at normal temperature; and a second seal part 60 for pressing the valve seat by heat expansion at high temperature environment while being elastically deformed by receiving a reaction force acting from the valve seat. A volume of the first seal part 58 is set to be smaller than a volume of the second seal part 60. A valve seat side edge part of the first seal part 58 is positioned nearer the valve seat than a valve seat side edge part of the second seal part 60.