A diaphragm for a speaker (1) is formed of a composite (15) containing a resin (16) and a bamboo fiber (17) included therein. This constitution can provide a diaphragm (1) which can simultaneously realize advantages of the bamboo fiber (17) such as a high sound quality and a high level of freedom in setting of property values of the diaphragm (1) and advantages of the resin diaphragm (1) such as improved moisture resistance reliability or strength, excellent appearance, and improved productivity and dimensional stability.