Reciprocal movement device

A forward/backward movement device comprising:

• a case provided with a through hole;
• a guide member that is housed and fixed in the case and includes a shaft and a protrusion formed on an outer peripheral surface of the shaft;
• a forward/backward movement member having a cylindrical shape body which includes a groove formed on an inner peripheral surface of the cylindrical body, in which the shaft is inserted and the protrusion is slidably fitted into the groove, a first end side of the forward/backward movement member being provided with a latch and being exposed to an outside, a second end side of the forward/backward movement member being inserted in the through hole in a state where the second end side is positioned inside of the case, and which is configured to move forward and backward with respect to the case while rotating by being guided by the protrusion;
• a seal cover disposed to encircle the though hole to close a gap between the case and the forward/backward movement member;
• a cam which is disposed at an outer peripheral side of the forward/backward movement member inside of the case without being exposed to the outside and which is configured to rotatably hold the forward/backward movement member and move forward and backward together with the forward/backward movement member;
• and
• a spring disposed inside of the case to connect with the cam and configured such that, when the spring extends, the spring pushes the cam to move the forward/backward movement member forward via the cam, and, when the forward/backward movement member moves backward, the spring is compressed by the forward/backward movement member via the cam.