The explosion mechanism of supernovae (SNe) is a longstanding mystery. Clarifying the multi-dimensional shape of the explosion by observations will give important constraints on the explosion mechanism. Among various kinds of observations, polarization measurement is the most direct method to study the geometry of a SN, an extragalactic point source. We have been conducting spectropolarimetric observations of stripped-envelope SNe with the Subaru telescope. We have detected linear polarization at various lines, undoubtedly indicating that the explosion is not spherically symmetric. We discuss possible explosion geometry to explain these features.