A telescopic, mobile crane comprising, a first base member pivotally mounted on a carriage, a second telescopic member telescopically engaged with the first member, an idle or manual member telescopically engaged to the second member and a drive piston and cylinder unit connected between the first and second members for extending the second member from the first member. An arresting apparatus is connected between the piston and cylinder arrangement and the idle member for extending the idle member. When the idle member is extended, the first and second members are locked to each other by a pawl and pin arrangement and the second member is disengaged from the piston and cylinder arrangement. After the idle member is extended, the first and second members are unlocked from each other to permit the extension of the second member.