Wavelength conversion element, light source device, and projector

A wavelength conversion element, comprising:

• a wavelength conversion layer which has a first face on which an excitation light is incident and a second face facing the first face;
• a first layer which is provided facing the second face and contains a first inorganic oxide;
• a second layer which is provided facing the first layer, contains either silver or aluminum, and reflects the excitation light or a light obtained by wavelength conversion of the excitation light by the wavelength conversion layer;
• a third layer which is provided facing the second layer and contains a first metal other than silver or aluminum;
• a fourth layer which is provided facing the third layer and contains the first inorganic oxide or a second inorganic oxide that is different from the first inorganic oxide;
• and a fifth layer which is provided facing the fourth layer and contains the first metal or a second metal that is different from the first metal;
• wherein the wavelength conversion element includes a substrate, and the fifth layer and the substrate are bonded to each other by a bonding material provided between the fifth layer and the substrate.