A method for installing a rigid constraint (g1, g2) in a heat resistant pipeline to resist a dynamic load while reducing use of snubbers, the pipeline being mounted with a plurality of snubbers at a plurality of positions to satisfy requirements for temperature and seismic operating conditions, the method comprising the following steps: a first calculation step, calculating to obtain a temperature deformation displacement of each point of the pipeline (ac, ad) after a part or an entirety of the snubbers is reduced from the pipeline; a second calculation step, calculating to obtain a modal result of the pipeline (ac, ad) and a dynamic response displacement of each point of the pipeline (ac, ad) after a part or an entirety of the snubbers is reduced from the pipeline, the modal result including all necessary natural frequencies and vibration modes of respective orders; an analysis step, determining a position at which the rigid constraint (g1, g2) is to be installed and a direction along which the rigid constraint (g1, g2) is to be applied based on both of the temperature deformation displacement and the dynamic response displacement of the pipeline (ac, ad) after a part or an entirety of the snubbers is reduced from the pipeline, wherein the position at which the rigid constraint (g1, g2) is to be installed is a position in which the dynamic response displacement is required to be reduced among respective points of the pipeline (ac, ad), and the direction along which the rigid constraint (g1, g2) is to be applied is any one in a plane perpendicular to a direction of the temperature deformation displacement at the position at which the rigid constraint is to be installed; a determination step, calculating a stress of the pipeline (ac, ad) after the rigid constraint (g1, g2) is applied and a reaction force of the rigid constraint (g1, g2) to determine whether the stress of the pipeline (ac, ad) and the reaction force of the rigid constraint (g1, g2) satisfy design requirements; and an installation step, when it is determined that the stress of the pipeline (ac, ad) and the reaction force of the rigid constraint (g1, g2) satisfy the design requirements, installing at least two rigid constraints (g1, g2) at said position and applying the at least two rigid constraints (g1, g2) along said direction to reduce a part or an entirety of the plurality of snubbers, wherein when the rigid constraints (g1, g2) are installed, an installation position point of each of the rigid constraints (g1, g2) on a building structure is moved in advance by a predetermined amount in the direction of the temperature deformation displacement. a first calculation step, calculating to obtain a temperature deformation displacement of each point of the pipeline (ac, ad) after a part or an entirety of the snubbers is reduced from the pipeline; a second calculation step, calculating to obtain a modal result of the pipeline (ac, ad) and a dynamic response displacement of each point of the pipeline (ac, ad) after a part or an entirety of the snubbers is reduced from the pipeline, the modal result including all necessary natural frequencies and vibration modes of respective orders; an analysis step, determining a position at which the rigid constraint (g1, g2) is to be installed and a direction along which the rigid constraint (g1, g2) is to be applied based on both of the temperature deformation displacement and the dynamic response displacement of the pipeline (ac, ad) after a part or an entirety of the snubbers is reduced from the pipeline, wherein the position at which the rigid constraint (g1, g2) is to be installed is a position in which the dynamic response displacement is required to be reduced among respective points of the pipeline (ac, ad), and the direction along which the rigid constraint (g1, g2) is to be applied is any one in a plane perpendicular to a direction of the temperature deformation displacement at the position at which the rigid constraint is to be installed; a determination step, calculating a stress of the pipeline (ac, ad) after the rigid constraint (g1, g2) is applied and a reaction force of the rigid constraint (g1, g2) to determine whether the stress of the pipeline (ac, ad) and the reaction force of the rigid constraint (g1, g2) satisfy design requirements; and an installation step, when it is determined that the stress of the pipeline (ac, ad) and the reaction force of the rigid constraint (g1, g2) satisfy the design requirements, installing at least two rigid constraints (g1, g2) at said position and applying the at least two rigid constraints (g1, g2) along said direction to reduce a part or an entirety of the plurality of snubbers, wherein when the rigid constraints (g1, g2) are installed, an installation position point of each of the rigid constraints (g1, g2) on a building structure is moved in advance by a predetermined amount in the direction of the temperature deformation displacement.