A control apparatus to control a work machine with an autonomous movement function, comprising: an illuminance information obtaining section (162, 164, 220, 364, 182) configured to obtain illuminance information indicating at least one of (i) an illuminance of the work machine in motion and (ii) an illuminance of a region located on an advancing direction of the work machine in motion; and a control section configured to control at least one of an advancing direction, an advancing speed, a travel mode, and a work mode of the work machine based on the illuminance information obtained by the illuminance information obtaining section, wherein the control section includes a change determination section (510, 650, 710) configured to determine whether to change an advancing direction of the work machine based on a predetermined algorithm if at least one of (i) an illuminance of the work machine in motion and (ii) an illuminance of a region located on an advancing direction of the work machine in motion which are indicated by the illuminance information obtained by the illuminance information obtaining section satisfy a predetermined condition; wherein the control section includes an instruction output section configured to output an instruction to change an advancing direction of the work machine if the change determination section determines to change an advancing direction of the work machine, wherein the control apparatus being characterised in that the change determination section is configured to determine whether to change an advancing direction of the work machine based on a probability model, and the probability model is designed such that a probability that an advancing direction is changed increases as (i) an illuminance of the work machine in motion or (ii) an illuminance of a region located on the advancing direction of the work machine in motion decreases; or that the probability that the advancing direction is changed in the probability model is defined based on a sunshine condition of each location within a work region of the work machine. an illuminance information obtaining section (162, 164, 220, 364, 182) configured to obtain illuminance information indicating at least one of (i) an illuminance of the work machine in motion and (ii) an illuminance of a region located on an advancing direction of the work machine in motion; and a control section configured to control at least one of an advancing direction, an advancing speed, a travel mode, and a work mode of the work machine based on the illuminance information obtained by the illuminance information obtaining section, wherein the control section includes a change determination section (510, 650, 710) configured to determine whether to change an advancing direction of the work machine based on a predetermined algorithm if at least one of (i) an illuminance of the work machine in motion and (ii) an illuminance of a region located on an advancing direction of the work machine in motion which are indicated by the illuminance information obtained by the illuminance information obtaining section satisfy a predetermined condition; wherein the control section includes an instruction output section configured to output an instruction to change an advancing direction of the work machine if the change determination section determines to change an advancing direction of the work machine, wherein the control apparatus being characterised in that the change determination section is configured to determine whether to change an advancing direction of the work machine based on a probability model, and the probability model is designed such that a probability that an advancing direction is changed increases as (i) an illuminance of the work machine in motion or (ii) an illuminance of a region located on the advancing direction of the work machine in motion decreases; or that the probability that the advancing direction is changed in the probability model is defined based on a sunshine condition of each location within a work region of the work machine.