[Object] The present invention provides a space vector modulation method for an AC-AC direct conversion device, which can convert input and output waveforms into sine waves and reduce the number of times of switching at an inter-sector shift.[Means to Solve] A vector state in which a line voltage of multi-phase AC output is expanded onto a two-phase static αβ coordinates is defined. Simple harmonic oscillation vector axes of a sector where an output voltage command value vector Vo* exists are defined as an X axis and a Y axis. Maximum/middle/minimum vectors in each axis, a zero vector that is an intermediate voltage of a phase voltage, and one rotation vector that is present in the sector, are set as base vectors. A switching selection pattern formed by a combination of four vectors among these vectors, which satisfies predetermined conditions, is determined by a selection means 15. On the basis of power source voltage information and output current information, an inverse matrix operation for the four vectors is executed by a duty operation means 14, and a duty solution of the four vectors is determined, then the input and output waveforms are simultaneously converted into the sine waves by the determined duties.