supplying signals of opposite phases and equal amplitude to the first transistor 2 and the second transistor 3 the base potential p3 of transistor 5 is set by the resistors 13 14 and 15 such that it is equal to vl vd constant when the output of the and gate 11 is 34 1 34 and lower than vl when the output of the and gate 11 is 34 0 34 when the input signals to the and gate 11 is 34 0 34 transistor 4 is turned on and transistor 5 is turned off in this case base potential pl of the transistor 2 is lower than v2 and base potential p2 of transistor 3 is essentially equal to v2 on the other hand when the input signals to the and gate 11 are 34 1 34 transistor 4 is turned off and transistor 5 is turned on in this case base potential pl of transistor 2 is essentially equal to v2 and base potential p2 of transistor 3 is lower than v2 the collector potential of the turn off transistor of transistors 4 and 5 is essentially equal to v2 because the collector current of the turn off transistor when it is turned on is sufficiently larger than.