A front loader configured to be detachably attached to a vehicle body, wherein: an attaching mechanism is provided for attaching the front loader to the vehicle body; the attaching mechanism includes a hook engageable with an attaching frame boss portion provided in the vehicle body; and the attaching mechanism is configured to attach to the front loader to the vehicle body with engagement of the hook with the attaching frame boss portion; and wherein a hook operational lever is provided for switching the hook to an engaging position engaged with the attaching frame boss portion or a non-engaging position not engaged with the attaching frame boss portion wherein the front loader further includes a pair of left and right booms that support an implement and a pair of left and right side frames that support base end portions of the booms to be pivotable about a pivot axis extending along the vehicle body left-right direction and that can be detachably attached to the vehicle body; wherein the side frames includes a par of left and right side plates; and wherein the hook operational lever is disposed between the pair of left and right side plates and can be manually operated from a driving section in which an operator rides; characterized in that the side frame includes a lever guide for the hook operational lever; the lever guide is constituted of a plate-like member that is bent appropriately; the lever guide defines a guide groove for guiding the hook operational lever; and the guide groove includes an engaging position positioning portion for fixing the hook operational lever at an engaging operational position corresponding to the engaging position of the hook, a non-engaging position positioning portion for fixing the hook at a non-engaging operational position corresponding to the non-engaging position of the hook, and a tilted guide portion extending between the engaging position positioning portion and the non-engaging position positioning portion, wherein at the non-engaging position positioning portion there is provided a retaining portion for hooking and retaining the hook operational lever at the non-engaging operational position. an attaching mechanism is provided for attaching the front loader to the vehicle body; the attaching mechanism includes a hook engageable with an attaching frame boss portion provided in the vehicle body; and the attaching mechanism is configured to attach to the front loader to the vehicle body with engagement of the hook with the attaching frame boss portion; and wherein a hook operational lever is provided for switching the hook to an engaging position engaged with the attaching frame boss portion or a non-engaging position not engaged with the attaching frame boss portion wherein the front loader further includes a pair of left and right booms that support an implement and a pair of left and right side frames that support base end portions of the booms to be pivotable about a pivot axis extending along the vehicle body left-right direction and that can be detachably attached to the vehicle body; wherein the side frames includes a par of left and right side plates; and wherein the hook operational lever is disposed between the pair of left and right side plates and can be manually operated from a driving section in which an operator rides; characterized in that the side frame includes a lever guide for the hook operational lever; the lever guide is constituted of a plate-like member that is bent appropriately; the lever guide defines a guide groove for guiding the hook operational lever; and the guide groove includes an engaging position positioning portion for fixing the hook operational lever at an engaging operational position corresponding to the engaging position of the hook, a non-engaging position positioning portion for fixing the hook at a non-engaging operational position corresponding to the non-engaging position of the hook, and a tilted guide portion extending between the engaging position positioning portion and the non-engaging position positioning portion, wherein at the non-engaging position positioning portion there is provided a retaining portion for hooking and retaining the hook operational lever at the non-engaging operational position. wherein the side frames includes a par of left and right side plates; and wherein the hook operational lever is disposed between the pair of left and right side plates and can be manually operated from a driving section in which an operator rides; characterized in that the side frame includes a lever guide for the hook operational lever; the lever guide is constituted of a plate-like member that is bent appropriately; the lever guide defines a guide groove for guiding the hook operational lever; and the guide groove includes an engaging position positioning portion for fixing the hook operational lever at an engaging operational position corresponding to the engaging position of the hook, a non-engaging position positioning portion for fixing the hook at a non-engaging operational position corresponding to the non-engaging position of the hook, and a tilted guide portion extending between the engaging position positioning portion and the non-engaging position positioning portion, wherein at the non-engaging position positioning portion there is provided a retaining portion for hooking and retaining the hook operational lever at the non-engaging operational position.