diff --git a/.changeset/fine-flies-drum.md b/.changeset/fine-flies-drum.md
new file mode 100644
index 00000000..fa3604e3
--- /dev/null
+++ b/.changeset/fine-flies-drum.md
@@ -0,0 +1,5 @@
+---
+'@vivliostyle/cli': patch
+---
+
+Fix error when input file is on different drive on Windows
diff --git a/src/server.ts b/src/server.ts
index b4d925b2..b5dcbd3d 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -122,12 +122,16 @@ export async function getSourceUrl({
   'viewerInput' | 'base' | 'workspaceDir' | 'rootUrl'
 >) {
   let input: string;
+  let isUrlPath = false;
   switch (viewerInput.type) {
     case 'webpub':
       input = viewerInput.manifestPath;
       break;
     case 'webbook':
       input = viewerInput.webbookEntryUrl;
+      // webbookEntryUrl is already a URL path (e.g., "/vivliostyle/test.html")
+      // or a full URL (e.g., "https://example.com/test.html")
+      isUrlPath = !isValidUri(input);
       break;
     case 'epub-opf':
       input = viewerInput.epubOpfPath;
@@ -145,10 +149,12 @@ export async function getSourceUrl({
   return (
     isValidUri(input)
       ? new URL(input)
-      : new URL(
-          upath.posix.join(base, upath.relative(workspaceDir, input)),
-          rootUrl,
-        )
+      : isUrlPath
+        ? new URL(input, rootUrl)
+        : new URL(
+            upath.posix.join(base, upath.relative(workspaceDir, input)),
+            rootUrl,
+          )
   ).href;
 }
 
diff --git a/src/util.ts b/src/util.ts
index 53883e22..ed4782e8 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -218,7 +218,8 @@ export function pathEquals(path1: string, path2: string): boolean {
 
 export function pathContains(parentPath: string, childPath: string): boolean {
   const rel = upath.relative(parentPath, childPath);
-  return rel !== '' && !rel.startsWith('..');
+  // If relative path is absolute (different drives on Windows), they are not related
+  return rel !== '' && !rel.startsWith('..') && !upath.isAbsolute(rel);
 }
 
 export function isValidUri(str: string): boolean {