1. A matrix converter space vector modulation method in which bidirectional switches of a matrix converter are PWM controlled in a space vector modulation, comprising: supposing line voltages of a multi-phase AC output to be states of vectors expanded on two-phase stationary αβ axes; defining a simple harmonic oscillation vector axis whose phase in a sector in which an output voltage command value V*o is present is retarded as X axis and the simple harmonic oscillation axis whose phase in the sector is advanced as Y axis; supposing maximum vectors X L , Y L , middle vectors X M ,Y M , and minimum vectors X S ,Y S on the respective axes, a zero vector Z which provides a middle voltage of phase voltages, and a rotation vector R which is present singly in the sector, to be eight base vectors; converting switching patterns for which virtual indirect space vectors are used into other switching patterns for which direct conversion space vectors constituted by a combination of five vectors among the eight base vectors are used; selecting any one of the converted switching patterns which satisfies predetermined conditions to reduce harmonics of an input current of the matrix converter and/or an output voltage thereof; calculating duties of the five space vectors which make a transit in the selected switching pattern from duty relationship equations between the virtual indirect space vectors and the direct conversion space vectors; and performing the PWM control for the bidirectional switches on a basis of the calculated duties.