There are provided a piezoelectric body of ytterbium-doped aluminum nitride, having a greater piezoelectric coefficient d33 or g33 than those not doped with ytterbium, and a MEMS device using the piezoelectric body. The piezoelectric body is represented by a chemical formula Al1-xYbxN where a value of x is more than 0 and less than 0.37 and having a lattice constant ratio c/a in a range of 1.53 or more and less than 1.6. The piezoelectric body with such a configuration has a greater piezoelectric coefficient d33 or g33 than those not doped with ytterbium.