A machining state information estimation device comprising: an information storage storing control information to be used in machining in an NC machine tool, information on a workpiece to be machined in the NC machine tool, and information on a tool to be used in the NC machine tool; a machining state information estimator configured to arrange, in a virtual space, a virtual workpiece set based on the information on the workpiece stored in the information storage and a virtual tool set based on the information on the tool stored in the information storage in such a manner that the virtual workpiece and the virtual tool have a positional relation identical to a positional relation based on the control information, and then relatively move the arranged virtual workpiece and virtual tool in accordance with the control information stored in the information storage and estimate a machining state that varies with time in virtual machining of the workpiece in accordance with relative movement of the workpiece and tool, wherein the machining state information estimator is configured to estimate, as the machining state information, machining state information including at least one selected from among information on a contact state between each cutting edge of the tool and the workpiece in a direction of contact depth between the tool and the workpiece, information on a contact state between each cutting edge of the tool and the workpiece in a direction of rotation of the tool, information on a cutting resistance applied to each cutting edge of the tool, information on surface roughness of the workpiece, and information on a cutting depth of each cutting edge of the tool in the direction of rotation of the tool; and an image data generator configured to, based on machining state information along time axis estimated by the machining state information estimator, generate image data for representing amounts of the machining state information along the time axis as an image. an information storage storing control information to be used in machining in an NC machine tool, information on a workpiece to be machined in the NC machine tool, and information on a tool to be used in the NC machine tool; a machining state information estimator configured to arrange, in a virtual space, a virtual workpiece set based on the information on the workpiece stored in the information storage and a virtual tool set based on the information on the tool stored in the information storage in such a manner that the virtual workpiece and the virtual tool have a positional relation identical to a positional relation based on the control information, and then relatively move the arranged virtual workpiece and virtual tool in accordance with the control information stored in the information storage and estimate a machining state that varies with time in virtual machining of the workpiece in accordance with relative movement of the workpiece and tool, wherein the machining state information estimator is configured to estimate, as the machining state information, machining state information including at least one selected from among information on a contact state between each cutting edge of the tool and the workpiece in a direction of contact depth between the tool and the workpiece, information on a contact state between each cutting edge of the tool and the workpiece in a direction of rotation of the tool, information on a cutting resistance applied to each cutting edge of the tool, information on surface roughness of the workpiece, and information on a cutting depth of each cutting edge of the tool in the direction of rotation of the tool; and an image data generator configured to, based on machining state information along time axis estimated by the machining state information estimator, generate image data for representing amounts of the machining state information along the time axis as an image.