A gas adsorption unit includes a getter, a package encapsulating the getter, and a low-melting member. The low-melting member is heated, and thereby melted, at a temperature lower than a melting point of the package to bond a connector including the low-melting member onto the package. Next, the low-melting member that has melted is cooled and cured. Then, thermal stress resulting from a difference in thermal expansion coefficient between the package and the connector is caused to the package connected to the connector, thereby breaking the package open.