To provide an automatic transmission allowing new addition of a one-way clutch effective in transmission shock measures while suppressing increase of an axial dimension of the automatic transmission.

This hydraulic controller for the belt type continuously variable transmission has a transmission mechanism part 100 comprising a belt 40 wound between a primary pulley 20 and a secondary pulley 30, a line pressure control means 210 controlling a line pressure PL supplied to the pulley 30 on the basis of a target variable speed ratio io, and a variable speed pressure control means 220 controlling a variable speed pressure Pc supplied to the pulley 20 on the basis of the variable speed ration io with the line pressure PL as an original pressure. When it is detected that an actual variable speed ratio i found from a primary rotation Npri and a secondary rotation Nsec accomplishes the target variable speed ratio io calculated by a control unit 1, the line pressure PL is reduced to an oil pressure PL(n)={PL(n-1)-α} that is smaller than the preceding line pressure PL(n-1) by a reduction margin α.