A water jet peening compressive residual stress test method comprising: holding a plastically deformable Almen strip under a predetermined underwater environment; and jetting water jet to the Almen strip, wherein the water jet peening compressive residual stress test method is performed in a water jet peening compressive residual stress test facility comprising: a water tank configured to form a predetermined underwater environment; a high-pressure water supply pipe configured to supply high-pressure water; and a high-pressure water pump configured to send high-pressure water to the high-pressure water supply pipe, wherein a water jet peening compressive residual stress test device is arranged in the underwater environment of the water tank, the high-pressure water supply pipe is connected to the water jet peening compressive residual stress test device and the high-pressure water pump, and a water jet peening compressive residual stress test is performed, wherein the water jet peening compressive residual stress test device comprises: a jet port mounting portion to which a jet port is mounted, the jet port being configured to jet the water jet; a high-pressure water pipe mounting portion provided communicating into the jet port mounting portion, and to which the high-pressure water supply pipe is mounted; and an Almen strip holding portion including a support surface facing the jet port mounting portion, and an attaching portion (44b, 44d) configured to allow a plate surface of a plastically deformable platelike Almen strip to be in contact with and attached to the support surface, wherein the attaching portion (44b, 44d) includes a pressing member including a through hole through which a portion of the Almen strip, to which the water jet is configured to be jetted, is let out, and a pressing surface configured to abut on an outer edge of the Almen strip, and a fixing member configured to fix the pressing member to sandwich the Almen strip between the pressing surface of the pressing member and the support surface, wherein a recessed portion configured to allow the Almen strip to be inserted to surround a vicinity of the Almen strip is included in at least one of the support surface and the pressing surface. holding a plastically deformable Almen strip under a predetermined underwater environment; and jetting water jet to the Almen strip, wherein the water jet peening compressive residual stress test method is performed in a water jet peening compressive residual stress test facility comprising: a water tank configured to form a predetermined underwater environment; a high-pressure water supply pipe configured to supply high-pressure water; and a high-pressure water pump configured to send high-pressure water to the high-pressure water supply pipe, wherein a water jet peening compressive residual stress test device is arranged in the underwater environment of the water tank, the high-pressure water supply pipe is connected to the water jet peening compressive residual stress test device and the high-pressure water pump, and a water jet peening compressive residual stress test is performed, wherein the water jet peening compressive residual stress test device comprises: a jet port mounting portion to which a jet port is mounted, the jet port being configured to jet the water jet; a high-pressure water pipe mounting portion provided communicating into the jet port mounting portion, and to which the high-pressure water supply pipe is mounted; and an Almen strip holding portion including a support surface facing the jet port mounting portion, and an attaching portion (44b, 44d) configured to allow a plate surface of a plastically deformable platelike Almen strip to be in contact with and attached to the support surface, wherein the attaching portion (44b, 44d) includes a pressing member including a through hole through which a portion of the Almen strip, to which the water jet is configured to be jetted, is let out, and a pressing surface configured to abut on an outer edge of the Almen strip, and a fixing member configured to fix the pressing member to sandwich the Almen strip between the pressing surface of the pressing member and the support surface, wherein a recessed portion configured to allow the Almen strip to be inserted to surround a vicinity of the Almen strip is included in at least one of the support surface and the pressing surface.