PURPOSE: To improve maintainability of configuration by performing a deformation processing of a polyolefine resin under a specific temperature after which the resin is kept for a certain time under a specific temperature while maintaining the configuration as it is and then cooled under a specific temperature while keeping the configuration as it is.

CONSTITUTION: After giving a polyolefine resin forming body a deformation process under the temperature of 60°C or higher but lower than the resin melting temperature, the resin is kept for a certain time under the temperature of 60°C or higher but lower than the resin melting temperature while holding the deformed configuration. Thereafter, the resin is cooled to the temperature lower by 30°C than the deformation temperature or the holding temperature, whichever is lower. The polyolefine resin formed body thus holding the deformed configuration is substantially restored to the configuration prior to deformation process by means of heating it to a temperature lower by 10°C than the deformation process temperature or the holding temperature, whichever is higher.