Diaphragm pump, liquid ejection head and liquid ejection apparatus

A diaphragm pump, comprising:

• a diaphragm that is deformable;
• a supporting member that supports the diaphragm;
• an opening portion that is in communication with a space formed between the diaphragm and the supporting member;
• and
• a check valve having a plate shape that is provided between the opening portion and the space and is configured to open and close an opening that is in communication with the opening portion,
• wherein the check valve has:
• a flap piece portion that opens and closes the opening;
• an outer peripheral portion that surrounds the flap piece portion and forms an outer shape of the check valve;
• and
• a flexible portion that connects the flap piece portion and the outer peripheral portion to each other,
• wherein the flexible portion bends to allow the flap piece portion to open and close the opening, and
• wherein the check valve includes a slit formed between the flap piece portion and the outer peripheral portion.