Micro-bubble generator and shower head

A micro-bubble generator comprising:

• an inner case comprising:
• a water inlet hole;
• a water discharging hole;
• and
• an inner ventilation window disposed along a water passage disposed between the water inlet hole and the water discharging hole;
• and
• an outer case disposed on an outer side of the inner case and comprising an outer ventilation window connected to the inner ventilation window,
• wherein the outer case is configured to make a sliding movement with an outer circumference surface of the inner case, and comprises an elastic body disposed in the outer case, the elastic body being in pressure contact with the outer circumference surface of the inner case and configured to make a sliding movement along the outer circumference surface of the inner case,
• wherein when the outer case makes the sliding movement, a first air inlet and a second air inlet are switched to and from each other,
• wherein the first air inlet is formed when the inner ventilation window and the outer ventilation window are displaced from each other, generating a gap between the outer circumference surface of the inner case and the elastic body and connecting the water passage to external air through the gap, and
• wherein the second air inlet is formed when the outer ventilation window is aligned with the inner ventilation window, connecting the water passage to the external air.