A construction machine comprising: a vehicle body (2, 4); an engine provided on said vehicle body and serving as a power source; a hydraulic pump driven by said engine and supplying a pressurized oil; a hydraulic actuator (5E-G) driven by the pressurized oil supplied from said hydraulic pump; and a lock device switched between a lock position prohibiting driving of said hydraulic actuator and an unlock position allowing the driving of said hydraulic actuator, wherein the lock device includes a gate lock lever which is at a lock position prohibiting driving of said hydraulic actuator at a raised position and at an unlock position allowing the driving of said hydraulic actuator at a lowered position, a power switch for starting said engine; wherein a work is performed by the driving of said hydraulic actuator in a state where said lock device is switched to the unlock position, characterized in that: a wireless authentication device provided on said vehicle body and performing wireless authentication with a portable key device; and a vehicle body controller allowing or prohibiting start of said engine on the basis of an operation of said power switch and authentication by said wireless authentication device are provided; said wireless authentication device is constituted to transmit an authentication request signal within an authenticable range and to perform authentication when an authentication signal replied from said portable key device is received on the basis of the transmitted authentication request signal; said vehicle body controller is constituted to allow start of said engine by said power switch when said lock device is switched to the raised lock position and said wireless authentication device performs authentication by said portable key device, said wireless authentication device is adapted to hold an authenticated state for a predetermined authentication holding time after the authentication signal replied from said portable key device is received; and a time setting unit is provided which can variably set said authentication holding time. a vehicle body (2, 4); an engine provided on said vehicle body and serving as a power source; a hydraulic pump driven by said engine and supplying a pressurized oil; a hydraulic actuator (5E-G) driven by the pressurized oil supplied from said hydraulic pump; and a lock device switched between a lock position prohibiting driving of said hydraulic actuator and an unlock position allowing the driving of said hydraulic actuator, wherein the lock device includes a gate lock lever which is at a lock position prohibiting driving of said hydraulic actuator at a raised position and at an unlock position allowing the driving of said hydraulic actuator at a lowered position, a power switch for starting said engine; wherein a work is performed by the driving of said hydraulic actuator in a state where said lock device is switched to the unlock position, characterized in that: a wireless authentication device provided on said vehicle body and performing wireless authentication with a portable key device; and a vehicle body controller allowing or prohibiting start of said engine on the basis of an operation of said power switch and authentication by said wireless authentication device are provided; said wireless authentication device is constituted to transmit an authentication request signal within an authenticable range and to perform authentication when an authentication signal replied from said portable key device is received on the basis of the transmitted authentication request signal; said vehicle body controller is constituted to allow start of said engine by said power switch when said lock device is switched to the raised lock position and said wireless authentication device performs authentication by said portable key device, said wireless authentication device is adapted to hold an authenticated state for a predetermined authentication holding time after the authentication signal replied from said portable key device is received; and a time setting unit is provided which can variably set said authentication holding time. a wireless authentication device provided on said vehicle body and performing wireless authentication with a portable key device; and a vehicle body controller allowing or prohibiting start of said engine on the basis of an operation of said power switch and authentication by said wireless authentication device are provided; said wireless authentication device is constituted to transmit an authentication request signal within an authenticable range and to perform authentication when an authentication signal replied from said portable key device is received on the basis of the transmitted authentication request signal; said vehicle body controller is constituted to allow start of said engine by said power switch when said lock device is switched to the raised lock position and said wireless authentication device performs authentication by said portable key device, said wireless authentication device is adapted to hold an authenticated state for a predetermined authentication holding time after the authentication signal replied from said portable key device is received; and a time setting unit is provided which can variably set said authentication holding time.