A vehicle pop-up hood device comprising: a pair of actuators respectively having a piston rod that, upon actuation, becomes extended from a cylinder toward the vehicle upper side and is configured to push up both vehicle width direction end portions of a hood; and a lock mechanism that: is disposed in the respective actuator and comprises: a housing groove portion formed along the circumferential direction of a piston portion is formed in an outer peripheral portion of the piston portion, and a retention groove portion that is formed in an inner peripheral portion of the cylinder along the circumferential direction of the cylinder, and that is configured to temporarily retain the piston rod extended from the cylinder in a retention position via a lock ring, wherein the lock ring is made of metal having an annular shape, is configured to be elastically deformable in its radial direction, is housed in the housing groove portion in a diameter-reduced state, and in the retention position becomes fitted into the retention groove portion, wherein cancellation of the temporary retention of the piston in the retention position occurs when a predetermined load acts on the piston rod toward the vehicle lower side, and whereby the lock mechanism is configured to deter movement of the piston rod toward the vehicle lower side as a result of the lock ring being placed in a lock position on the vehicle lower side of the retention position on the lower end side of the cylinder with respect to the retention groove portion. a pair of actuators respectively having a piston rod that, upon actuation, becomes extended from a cylinder toward the vehicle upper side and is configured to push up both vehicle width direction end portions of a hood; and a lock mechanism that: is disposed in the respective actuator and comprises: a housing groove portion formed along the circumferential direction of a piston portion is formed in an outer peripheral portion of the piston portion, and a retention groove portion that is formed in an inner peripheral portion of the cylinder along the circumferential direction of the cylinder, and that is configured to temporarily retain the piston rod extended from the cylinder in a retention position via a lock ring, wherein the lock ring is made of metal having an annular shape, is configured to be elastically deformable in its radial direction, is housed in the housing groove portion in a diameter-reduced state, and in the retention position becomes fitted into the retention groove portion, wherein cancellation of the temporary retention of the piston in the retention position occurs when a predetermined load acts on the piston rod toward the vehicle lower side, and whereby the lock mechanism is configured to deter movement of the piston rod toward the vehicle lower side as a result of the lock ring being placed in a lock position on the vehicle lower side of the retention position on the lower end side of the cylinder with respect to the retention groove portion. a housing groove portion formed along the circumferential direction of a piston portion is formed in an outer peripheral portion of the piston portion, and a retention groove portion that is formed in an inner peripheral portion of the cylinder along the circumferential direction of the cylinder, and that is configured to temporarily retain the piston rod extended from the cylinder in a retention position via a lock ring, wherein the lock ring is made of metal having an annular shape, is configured to be elastically deformable in its radial direction, is housed in the housing groove portion in a diameter-reduced state, and in the retention position becomes fitted into the retention groove portion, wherein cancellation of the temporary retention of the piston in the retention position occurs when a predetermined load acts on the piston rod toward the vehicle lower side, and whereby the lock mechanism is configured to deter movement of the piston rod toward the vehicle lower side as a result of the lock ring being placed in a lock position on the vehicle lower side of the retention position on the lower end side of the cylinder with respect to the retention groove portion.