the 2 3 relay valve 290 the spool 291 is shifted upward by spring 292 thereby connecting passage 112b to passage 117 the passage 117 communicates to the lock up shift control valve 300 the spool 301 of the lock up shift control valve 300 is disposed under the control of the governor pressure acting in the chamber 303 so that the spool is shifted upward by spring 302 when the governor pressure is below the predetermined value p 1 whereas the spool is shifted downward against the force of spring 302 when the governor pressure has increased beyond the value p 1 thereby connecting oil passage 117 to passage 118 the passage 118 communicates to the chamber 284 of the lock up shift valve 280 when the oil pressure in the passage 112b has gradually increased to be above a predetermined value the piston in the oil pressure cylinder 400 is actuated to engage the brake 13 when the pressure in the passage 112b has further increased so far that the difference between the pressure and the line pressure acting in the chamber 283 becomes smaller than the predetermined value p a if the governor pressure in passage 111 has also become the predetermined value p 1 the oil pressure in passage 112b is supplied to the chamber 284 of the lock up shift valve 280 thereby driving the spool 281 upward thereby connecting passages 103 and 120 then the oil pressure in the passage 103 is supplied to passage 120 thus putting the lock up clutch 6 into engagement.