  We consider the long standing problem in field theories of bosons that the
boson vacuum does not consist of a `sea', unlike the fermion vacuum. We show
with the help of supersymmetry considerations that the boson vacuum indeed does
also consist of a sea in which the negative energy states are all "filled",
analogous to the Dirac sea of the fermion vacuum, and that a hole produced by
the annihilation of one negative energy boson is an anti-particle. This might
be formally coped with by introducing the notion of a double harmonic
oscillator, which is obtained by extending the condition imposed on the wave
function. Next, we present an attempt to formulate the supersymmetric and
relativistic quantum mechanics utilizing the equations of motion.
