To provide a switch drive unit that operates in a wide input voltage range, and prevents the variation in the characteristic of a switching element.

This switch drive unit 100 includes: a predriver 10 which pulse-drives a control voltage SG of the switching element 11 between an upper-side drive voltage VH and a lower-side drive voltage VL; withstand-voltage protection circuits (18 to 23) which draw in drive currents of the predriver 10 while controlling the lower-side drive voltage VL according to an input voltage Vin so that a voltage difference between the input voltage Vin and the control voltage SG is maintained not higher than a prescribed value; a low-voltage detection circuit 25 which detects whether the input voltage Vin is lowered below a threshold voltage; and a low-voltage driver 24 which draws in the drive current of the predriver 10 by lowering the lower-side drive voltage VL of the predriver 10 lower than a voltage at a normal time only when it is detected that the input voltage Vin is in a low-voltage state in the low-voltage detection circuit 25.