Method for mounting or demounting a mobile crane, comprising an auxiliary boom arranged on the head of the main boom of the mobile crane, and an auxiliary device for setting up the lower and upper luffing support connected to the adjustable auxiliary boom, wherein - a setting-up frame is connected as the auxiliary device to the lower luffing support, - a connecting rod strand can be connected to the lifting cable of the main lifting gear on the one hand and - is articulated on the tip of the lower luffing support on the other hand, and - a tensile member strand is provided between the lower luffing support and the upper luffing support, characterized in that: a) during mounting - the lifting cable is unwound from the main lifting gear of the mobile crane and connected to the multi-member connecting rod strand, - by winding the lifting cable onto the lifting gear, the setting-up frame begins to draw up automatically, and the connecting rod strand begins to tauten first to the right of the setting-up frame, then also to the left of the setting-up frame until the lower luffing support is also raised, - the main lifting gear winds up further, and the tensile member strand between the luffing supports (8 and 9) begins to tauten, specifically to a point until - the connecting rod strand has reached its end position in front of the main lifting gear and the luffing supports (8 and 9) are in the end position, b) during demounting, the preceding steps are performed in the reverse order. - a setting-up frame is connected as the auxiliary device to the lower luffing support, - a connecting rod strand can be connected to the lifting cable of the main lifting gear on the one hand and - is articulated on the tip of the lower luffing support on the other hand, and - a tensile member strand is provided between the lower luffing support and the upper luffing support, a) during mounting - the lifting cable is unwound from the main lifting gear of the mobile crane and connected to the multi-member connecting rod strand, - by winding the lifting cable onto the lifting gear, the setting-up frame begins to draw up automatically, and the connecting rod strand begins to tauten first to the right of the setting-up frame, then also to the left of the setting-up frame until the lower luffing support is also raised, - the main lifting gear winds up further, and the tensile member strand between the luffing supports (8 and 9) begins to tauten, specifically to a point until - the connecting rod strand has reached its end position in front of the main lifting gear and the luffing supports (8 and 9) are in the end position, - the lifting cable is unwound from the main lifting gear of the mobile crane and connected to the multi-member connecting rod strand, - by winding the lifting cable onto the lifting gear, the setting-up frame begins to draw up automatically, and the connecting rod strand begins to tauten first to the right of the setting-up frame, then also to the left of the setting-up frame until the lower luffing support is also raised, - the main lifting gear winds up further, and the tensile member strand between the luffing supports (8 and 9) begins to tauten, specifically to a point until - the connecting rod strand has reached its end position in front of the main lifting gear and the luffing supports (8 and 9) are in the end position, b) during demounting, the preceding steps are performed in the reverse order.