Protection circuit

A protection circuit for preventing application of voltage in a reverse direction to a circuit unit having a predetermined function, comprising:

• a power supply terminal;
• a ground terminal;
• and
• first to third transistors,
• wherein:
• the first transistor has one of a source and a drain connected to the power supply terminal and a gate connected to the ground terminal and has the other one of the source and drain connected to a first region including a region where a channel is to be formed in the first transistor;
• the second transistor has one of a source and a drain connected to a second region including a region where a channel is to be formed in the second transistor and the other one of the source and drain of the first transistor, a gate connected to the power supply terminal, the other one of the source and drain connected to the ground terminal;
• the third transistor has one of a source and a drain connected to the power supply terminal, a gate connected to the ground terminal, the other one of the source and drain connected to the ground terminal through the circuit unit;
• and
• the first region and the second region are integrally formed and are connected to a third region including a region where a channel is formed in the third transistor.